General aviation approach and landing practices

- _

P r e s t i g e E l i t e GENERAL AVIATION APPROACH AND LANDING PRACTICES Loyd C. Parker N A S A Wallops F l i g h t Center Maxwell W. Goode NASA Langley Research Center S U M M A R Y The c h a r a c t e r i s t i c s of air t r a f f i c p a t t e r n s a t uncontrolled a i r p o r t s and techniques used by a group of g e n e r a l a v i a t i o n p i l o t s i n landing l i g h t a i r p l a n e s have been documented. The r e p o r t c o n t a i n s t h e r e s u l t s of some 1600 r a d a r t r a c k s taken a t f o u r uncontrolled a i r p o r t s and some 600 landings made by 22 p i l o t s i n two, four-place, single-engine l i g h t a i r p l a n e s . The r e s u l t s show t h a t t h e u n c o n t r o l l e d t r a f f i c p a t t e r n is h i g h l y v a r i a b l e . The a l t i t u d e s , d i s t a n c e s , and p i l o t i n g procedures u t i l i z e d may a f f e c t t h e a b i l i t y f o r p i l o t s t o see-and-avoid i n t h i s environment. Most landing approaches were conducted a t an a i r s p e e d above recommended, r e s u l t i n g i n s i g n i f i c a n t f l o a t i n g during f l a r e and touchdowns t h a t were r e l a t i v e l y f l a t and o f t e n nose-low.

INTRODUCTION The National Aeronautics and Space Administration h a s undertaken r e s e a r c h programs t o document t h e p r a c t i c e s used by g e n e r a l aviatior?

p i l o t s i n t h e t r a f f i c p a t t e r n and d u r i n g f i n a l approach and landing.

These e f f o r t s were prompted by t h e g e n e r a l a v i a t i o n safety records r e f l e c t e d i n a c c i d e n t summary r e p o r t s , r e f e r e n c e 1, and mid-air c o l l i s i o n r e p o r t s , r e f e r e n c e s 2, 3, and 4. These r e p o r t s i n d i c a t e t h a t t h e most f r e q u e n t a c c i d e n t s , under v i s u a l f l i g h t r u l e s (VFR), occur a t t h e a i r p o r t during t h e approach and landing of single-engine l i g h t p l a n e s flown f o r pleasure. A d d i t i o n a l l y , most mid-air c o l l i s i o n s occur i n t h e t r a f f i c p a t t e r n a t uncontrolled a i r p o r t s on f i n a l approach and involve l a c k of adherence t o proper p a t t e r n procedures and f a i l u r e of p i l o t s t o see-and- avoid. The v a s t m a j o r i t y of a l l a c c i d e n t s are attriDUted t o t h e p i l o t , as t h e cause o r a f a c t o r c o n t r i b u t i n g t o t h e a c c i d e n t .

For t h e a i r t r a f f i c p a t t e r n s t u d i e s a t r a c k i n g radar system was used t o measure and record t h e position-time h i s t o r i e s of g e n e r a l a v i a t i o n a i r p l a n e s on p a t t e r n e n t r y and i n t h e p a t t e r n l e g s . Data were c o l l e c t e d a t f o u r uncontrolled a i r p o r t s each having a d i f f e r e n t environment and Airplane s e p a r a t i o n d a t a i n t h e p a t t e r n was measured p a t t e r n procedures.

a t t h e last a i r p o r t v i s i t e d using two r a d a r systems. For each radar t r a c k , t h e runway, type a i r p l a n e , s u r f a c e winds, barometric p r e s s u r e , v i s i b i l i t y , and cloud c e i l i n g s were a l s o recorded. Approximately 1400 i n d i v i d u a l r a d a r t r a c k s were taken t o d e f i n e a i r t r a f f i c p a t t e r n c h a r a c t e r - istics and 200 r a d a r t r a c k s taken t o d e f i n e normal g e n e r a l a v i a t i o n s e p a r a t i o n p r a c t i c e s . P r e l i m i n a r y r e s u l t s of t h e a i r t r a f f i c p a t t e r n s t u d i e s were r e p o r t e d i n r e f e r e n c e 5.

Two modern, four-place, single-engine l i g h t a i r p l a n e s (a low-wing and a high-wing) were l e a s e d from a fixed-based o p e r a t o r (FBO) and i n s t r u - mented t o o b t a i n f i n a l approach and l a n d i n g performance d a t a . A c a d r e of 22 g e n e r a l a v i a t i o n p i l o t s w i t h v a r i o u s backgrounds and e x p e r i e n c e was provided by t h e FBO t o perform a series of l a n d i n g s on a long runway

and a s h o r t runway ( 7 6 2 m - 2500 f t ) . Approach and

(1524 m - 5000 f t )

l a n d i n g d a t a were c o l l e c t e d using t h e instrumented a i r c r a f t and a ground tracking system f o r approximately 150 l a n d i n g s of each a i r p l a n e a t each runway. A l l p i l o t s were b r i e f e d on t h e purpose of t h e s t u d y and o p e r a t i o n of t h e equipment p r i o r t o p a r t i c i p a t i n g i n t h e program. P i l o t s were asked t o t u r n on t h e a i r b o r n e d a t a system j u s t p r i o r t o f i n a l approach and t o make normal l a n d i n g s based on t h e i r t r a i n i n g and experience. Each p i l o t was scheduled t o make a maximum of s i x l a n d i n g s i n one day on one runway. To a l l e v i a t e L r a f f i c c o n j e s t i o n on t h e long runway, touch-and-go l a n d i n g s w i t h a s i g n i f i c a n t ground r o l l were p e r m i t t e d . A l l l a n d i n g s on t h e s h o r t runway were completed t o a f u l l s t o p . P r e l i m i n a r y results of t h e low-wing a i r c r a f t phase of t h e approach and l a n d i n g s t u d y were p r e s e n t e d i n r e f e r e n c e 6.

TEST EQUIPMENT A i r t r a f f i c p a t t e r n measurements i n t h e u n c o n t r o l l e d a i r p o r t environ- ment were made u t i l i z i n g t h e MI'S-19 t r a c k i n g r a d a r s y s t s , f i g u r e 1.

Position-time h i s t o r i e s of a r r i v i n g a i r p l a n e s were recorded (iii magnetic t a p e a t one sample-per-second. O p e r a t o r s maintained a l o g of each t r a c k which included a c t i v e runway, type a i r p l a n e , s u r f a c e wind, c e i l i n g and v i s i b i l i t y d a t a . Radar d a t a were r o t a t e d t o t h e magnetic b e a r i n g of t h e t o t h e l a n d i n g runway t h r e s h o l d t o create a l a n d i n g runway and p a r a l l a x e d normalized runway r e f e r e n c e d c o o r d i n a t e s y s t e m which p e r m i t s d i r e c t comparison of p a t t e r n l e g s a t each a i r p o r t . During d a t a r e d u c t i o n , o p e r a t o r l o g d a t a were combined w i t h each t r a c k and s t o r e d on computer d i s c f i l e s f o r r e t r i e v a l and a n a l y s i s . P o s i t i o n accuracy of t h e r a d a r i n angles.

system is +, 9 . 5 m (10 yds) RMS i n range and +_ 1 m i l RMS

F i n a l approach and landing d a t a were obtained u s i n g two instrumented a i r p l a n e s , f i g u r e 2, and a ground t r a c k i n g system, f i g u r e 3. Both a i r p l a n e s , widely used i n g e n e r a l a v i a t i o n p r i v a t e f l y i n g , were l e a s e d from an FBO 2 1 d i f f e r e n t f l i g h t parameters, and instrumented t o measure and record i n c l u d i n g a i r s p e e d , p i t c h a t t i t u d e , f l a p p o s i t i o n , and a l t i t u d e . Modifi- c a t i o n s t o t h e a i r p l a n e s included a test boom on t h e l e f t wing t i p t o measure a i r s p e e d , a n g l e of a t t a c k and a n g l e of s i d e s l i p ; c o n t r o l s w i t c h e s on the instrument panel; and an instrumentation package located aft of The airborne data system increased the basic weight of the pilot’s seat.

the test airplanes approPimately 06.2 kilograms (190 pounds). Both airplanes were flight tested by NASA research pilots before and after modification with the determination that the instrumentation had a negligible effect on the airplane handling characteristics.

The ground tracking system was used to obtain the flight path and touchdown data with respect to the runway. This system was comprised of a 16-mm motion picture camera and a 3.05 m (10 ft) high by 67.0 m (220 ft) long photographic grid. The grid consisted of a series of vertical and horizontal plastic strips which formed squares of 0.6 m ( 2 ft) on a side within the grid frame. Normal photogrammetric techniques were used tc obtain the trajectory data from the motion picture film. The airplanes were assumed to be aligned with the runway center line for photographic A field survey of a typical grid installation indicated a analysis.

tracking accuracy of - + 0.3 m (2 1 ft) or less.

AIRPORTS AND RUNWAYS The location of the airports where data was taken during these studies are shown in figure 4 . Air traffic pattern data were collected at Salisbury-Wicomico (SBY), Gaithersburg ( G A I ) , Hyde (HYD), and Manassas (MAN) airports. Approach and landing data were collected at Hummel and Patrick Henry airports.

The Salisbury-Wicomico airport is located near Salishry, Maryland, in a rural, low density traffic environment and has an airport elevation of 15.5 m (51 ft) above mean-sea-level (MSL), traffic pattern altitude

(TPA) of 244 m (800 ft) , three 1524 m (5000 f t ) runways, an FAA Blight

Service Station (FSS), VOR facility, commuter service, active flight school, airplane maintenance and service facilities, and approximately 25,000 operations per year of which one-third are estimated to be twin- engine aircraft. The Gaithersburg, Maryland, airport is located in a high density traffic environment north of the Washington, D.C., Terminal Control Area (TCA) and has an airport elevation of 165 m (540 ft) MSL, TPA of 183 m (600 ft), one 960 m (3150 ft) runway, right-hand pattern for runway 31, active flight school, significant airplane maintenance facilities, large number of resident private and corporate airplanes, and operations estimated at 50,000 per year of which 09% are single-engine airplanes.

The Hyde airport is located near Clinton, Maryland, beneath the 457 m (1500 ft) floor of the Washington, D.C., TCA whose surface boundaries north, east, and west require all VFR traffic to enter from a south to The airport has an elevation of 76 m (249 ft) MSL, southwest direction.

TPA of 244 m (800 ft), two runways -.one of 976 m (3200 ft) and one of 640 m (2100 ft), another uncontrolled airport located approximately 1.5 n. mi. to the west, local pattern procedures which specify upwind pattern l e g e n t r y f o r runways 5 and 31, a c t i v e f l i g h t s c h o o l and f l y i n g c l u b , l a r g e number of r e s i d e n t a i r p l a n e s , s e r v i c e and maintenance f a c i l i t i e s , and o p e r a t i o n s estimated a t 25,000 p e r year of which 94% are s i n g l e - engine a i r p l a n e s . The Manassas, V i r g i n i a , (MAN) a i r p o r t is l o c a t e d west of t h e Washington, D.C., TCA i n a r e l a t i v e l y low d e n s i t y t r a f f i c environment and has an e l e v a t i o n of 57 m (186 f t ) , TPA of 244 m (800 f t ) , one 1128 m (3700 f t ) runway, commuter service, f l i g h t school, s e r v i c e and maintenance f a c i l i t i e s , l a r g c number of r e s i d e n t a i r p l a n e s and o p e r a t i o n s estimated a t 25-35,000 per year.

A2proach and landing d a t a f o r a long runway of 1524 m (5000 f t ) were c o l l e c t e d on runway 2 and LO a t t h e P a t r i c k Henry a i r p o r t i n Newport News, V i r g i n i a . The e l e v a t i a n of t h e a i r p o r t is 12.5 m ( 4 1 f t ) MSL and c o n t r o l l e d t r a f f i c a t t h e a i r ? o r t w a s very heavy a t times n e c e s s i t a t i n g extended downwind and long s t r a i g h t - i n f i n a l approach l e g s . The s h o r t runway a i r p o r t , Hummel, l o c a t e d near Saluda, V i r g i n i a , is a small uncon- t r o l l e d a i r p o r t w i t h a n e l e v a t i o n of 9 . 1 m (30 f t ) s e r v i n g a r u r a l area.

A l l landings were made on runway 18 which is 762 m (2500 f t ) long. F i n a l approach t o t h e runway is over water with a tree l i n e approximately one- q u a r t e r of a n i l e from t h r e s h o l d . The a i r p o r t had very l i g h t t r a f f i c ; consequently, t h e t e s t s u b j e c t s could f l y t h e p a t t e r n without i n t e r f e r e n c e .

RESTJLTS AND DISCUSSIONS The r e s u l t s of t h e uncontrolled a i r t r a f f i c p a t t e r n rreasurements s t u d y are based on a t o t a l of 1409 i n d i v i d u a l r a d a r t r a c k s a t t h r e e a i r p o r t s and 208 r a d a r t r a c k s of a i r p l a n e s e p a r a t i o n d i s t a n c e a t one a i r p o r t . Of t h e i n d i v i d u a l t r a c k s obtained approximately 83% were s i n g l e - engine a i r p l a n e s and 1 7 % were twin-engine a i r p l a n e s . The r e s u l t s of t h e approach and landing performance study covers a t o t a l of 616 landings made by both a i r p l a n e s a t both runways. A t o t a l of 299 landings (144 long runway, 155 s h o r t runway) were made i n t h e low-wing a i r p l a n e and 307 (163 long runway, 154 s h o r t runway) were made i n t h e high-wing a i r p l a n e .

Uncontrolled A i r T r a f f i c P a t t e r n The g e n e r a l l y recognized standard uncontrolled a i r t r a f f i c p a t t e r n is c h a r a c t e r i z e d by e n t r y t o the downwind l e g a t a 45-degree a n g l e a t a 244 m (800 f t ) a l t i t u d e above ground l e v e l (AGL) and "left-hand" t u r n s from downwind t o base and base t o f i n a l l e g s , r e f e r e n c e 7 . A d i f f e r e n t p a t t e r n may be adopted a t an i n d i v i d u a l a i r p o r t t o avoid a l o c a l problem.

Two of the a i r p o r t s had l o c a l v a r i a t i o n s from t h e s t a n d a r d p a t t e r n . HYD has a l o c a l procedure of an upwind p a t t e r n l e g e n t r y f o r runways 31 and 5. GAT has a l o c a l p a t t e r n a l t i t u d e of 183 m (600 f t ) and a right-hand p a t t e r n f u r runway 31. A t t h e time t r a f f i c measurements were conducted t h e FAA had issued NPRM 71-20, "Operations a t A i r p o r t s Without Control Towers," which proposed a new uncontrolled t r a f f i c p a t t e r n concept, f i g u r e 5 . FSS personnel a t S B Y encouraged l o c a l p i l o t s t o t r y o u t t h i s proposal during t h e p e r i o d a i r t r a f f i c measurements were conducted.

P a t t e r n Entry The l a c k of adherence t o p a t t e r n e n t r y procedures is a p o s s i b l e cause of mid-air c o l l i s i o n s . The p a t t e r n l e g e n t r y l o c a t i o n s were examined t o determine t h e v a r i a t i o n s from l o c a l procedure. The r e s u l t s of t h i s a n a l y s i s f o r a r r i v i n g a i r p l a n e s , f i g u r e 6, i l l u s t r a t e s t h e v a r i a t i o n s from l o c a l p a t t e r n e n t r y procedure. I n t h e higher t r a f f i c d e n s i t y environ- ment of G A I , adherence t o t h e pattern procedure was s i g n i f i c a n t l y b e t t e r than e i t h e r HYD o r S B Y . Approximately 51% at S B Y , 1 2 % f o r downwind and 6 t % f o r upwind runways a t HYD, and 11% a t G A I of t h e a r r i v i n g t r a f f i c d i d n o t adhere t o t h e l o c a l p a t t e r n e n t r y procedure. Normal l e f t - and r i g h t - hand t r a f f i c e n t e r i n g downwind a t G A I a r e shown a s a right-hand e n t r y on f i g u r e 6 t o i l l u s t r a t e d e v i a t i o n s from t h e s t a n d a r d . A t G A I 2% of t h e t r a f f i c f a i l e d t o recognize t h e right-hand p a t t e r n e s t a b l i s h e d f o r runway 31 and used a left-hand approach o p p o s i t e t o l o c a l p a t t e r n . A t S B Y 4% of t h e t r a f f i c used a right-hand base e n t r y o p p o s i t e t o t h e left-hand p a t t e r n .

P a t t e r n Leg D i s t r i b u t i o n s I n a d d i t i o n t o t h e v a r i a t i o n i n p a t t e r n e n t r y l o c a t i o n , t h e d i s t a n c e and a l t i t u d e v a r i a t i o n s w i t h i n t h e p a t t e r n l e g s may i n c r e a s e t h e p i l o t ' s see-and-avoid problem. The ground t r a c k d i s t r i b u t i o n s observed i n t h e p a t t e r n l e g s a t S B Y and HYD, f i g u r e 7 , i l l u s t r a t e t h i s v a r i a t i o n between a low d e n s i t y ( S B Y ) and high d e n s i t y (HYD) environment. Another f a c t o r a f f e c t i n g t h i s d i f f e r e n c e is t h a t S B Y ' s t r a f f i c was 33% twin-engine as compared t o only 6% twin-engine t r a f z i c of HYD. I n e i t h e r c a s e , t h e few t e n t h s of a n a u t i c a l mile o u t p a t t e r n l e g s a r e wide and extend from a t o g r e a t e r than 1.5 n. m i . from t h e runxay. General a v i a t i o n p i l o t s should expect c o n f l i c t i n g t r a f f i c a t d i s t a n c e s up t o s e v e r a l n a u t i c a l miles when e n t e r i n g a n uncontrolled t r a f f i c p a t t e r n . The LJmulative d i s t r i b u t i o n s of d i s t a n c e f o r t h e downwind, base and f i n a l p a t t e r n l e g s are sham i n f i g u r e 8. T h i s f i g u r e f u r t h e r i l l u s t r a t e s t h e d i f f e r e n c e between H Y D ' s c o n s t r a i n e d environment and S B Y . Conversely, t h e downwind cumulative d i s t r i b u t i o n , f i g u r e 8a, for S B Y and G A I , which h a s twice t h e t r a f f i c of S B Y , are e s s e n t i a l l y t h e same o u t t o t h e median p a t t e r n d i s t a n c e .

The divergence beyond t h e median f o r t h e S B Y and G A I suggest t h a t t h i s p o r t i o n of t h e d i s t r i b u t i o n may be a r e s u l t of t h e twin-engine t r a f f i c percentage of 33% a t S B Y and 11% a t G A I . On base and f i n a l l e g s l i t t l e d i f f e r e n c e i n t h e cumulative d i s t r i b u t i o n is shown up t o t h e 97% l e v e l , f i g u r e 8b and 8c.

T r a f f i c P a t t e r n A l t i t u d e V a r i a t i o n A f a c t o r which may s e r i o u s l y i n f l u e n c e a p i l o t ' s a b i l i t y t o d e t e c t another a i r p l a n e is adherence t o t h e e s t a b l i s h e d TPA. The cumulative d i s t r i b u t i o n s of t h e average a l t i t u d e f o r a l l t r a f f i c a t each a i r p o r t on ind, base and f i n a l l e g s are compared i n f i g u r e 9. The v a r i a t i o n E o m t e downwind TPA of 183 m (600 f t ) a t G A I and 244 m (800 f t ) a t HYD

n nd SB is shown i n f i g u r e 9a. Less than 1% of t h e t r a f f i c observed on

downwind is below an a l t i t u d e of approximately 122 m (400 f t ) . This f i g u r e a l s o i l l u s t r a t e s t h a t 99% of t h e t r a f f i c on downwind f o r G A I and HYD was below 305 m (1000 f t ) and a t SBY was below 430 m (1410 f t ) .

V a r i a t i o n s of a t least 183 m (600 f t ) o r g r e a t e r i n t h e TPA flown are shown a t a l l a i r p o r t s . A t HYD and SBY w h e r e t h e TPA was 244 m (800 f t ) , g r e a t e r than 65% (SBY) and 90% (HYD) of t h e t r a f f i c was below t h i s a l t i t u d e GAT media; a l t i t u d e is e s s e n t i a l l y on downwind l e g . I n comparison t h e equal t o t h e s p e c i f i e d TPA, i n d i c a t i n g t h a t 183 m (600 f t ) may b e t h e more n a t u r a l p a t t e r n a l t i t u d e . I n r e f e r e n c e 8, p i l o t s overwhelmingly i n d i c a t e d they p r e f e r r e d a TPA of 244 m (800 f t ) o r 305 m (1000 f t ) .

Most p i l o t s (95%) i n d i c a t e d they d i d n o t d e v i a t e from t h e TPA more than 45.6 m (150 f t ) , s u b s t a n t i a l l y less than was a c t u a l l y observed. The s i g n i f i - cant a l t i t u d e v a r i a t i o n s on downwind l e g are continued through base and f i n a l l e g s as shown on f i g u r e s 9b and 9c. Most d a t a shown f o r t h e f i n a l l e g were taken a t a d i s t a n c e g r e a t e r than 762 m (2500 f t ) from t h e runway threshold.

Croswind Leg Departure a i r p l a n e s may p a s s through p o r t i o n s of t h e crosswind l e g c r e a t i n g p o t e n t i a l mid-air c o l l i s i o n (MAC) s i t u a t i o n . This is i l l u s t r a t e d by f i g u r e 20 which shows a c r o s s s e c t i o n of a b i v a r i a t e log-normal d i s t r i - b u t i o n of t h e crosswind l e g a t SBY and t y p i c a l d e p a r t u r e p a t h s of a single-engine and twin-engine a i r p l a n e . The c o n f l i c t between d e p a r t i n g and a r r i v i n g a i r p l a n e s has been recognized. The l a t e s t FAA Advisory C i r c u l a r AC 90-60 "Recommended Standard T r a f f i c P a t t e r n s f o r A i r l i n e Operations a t Uncontrolled Airports", r e f e r e n c e 9 , recommends t h a t a downwind e n t r y mid-point of t h e runway be used and e s t a b l i s h e d s p e c i f i c d e p a r t u r e procedures t c minimize c o n f l i c t w i t h t r a f f i c using t h e crosswind l e g . A t a i r p o r t s where a crosswind p a t t e r n l e g is u t i l i z e d , s p e c i f i c are needed f o r a r r i v a l and touch-and-go t r a f f i c .

procedures Type of A i r c r a f t A comparison of t h e mean d i s t a n c e and a l t i t u d e f o r single-engine

high-wing (SEHW) , single-engine low-wing (SELW) , and twin-engine ( T W I N )

a i r p l a n e s a t SBY i s shown i n f i g u r e 11. The mean p a t t e r n d i s t a n c e , f i g u r e l l a , of t h e SEHW a i r p l a n e s Is approximately 0.2 n. m i . less than SELW a i r p l a n e s , and up t o 0.5 n. m i . less than TWINS on base l e g . TWINS were a l s o found t o f l y above S E H W and S E L W a i r p l a n e s on a l l p a t t e r n l e g s , f i g u r e l l b , except base and f i n a l where TWINS t r a n s i t i o n e d t o t h e lowest mean a l t i t u d e . I n t h e higher d e n s i t y environment of G A I and HYD, t h e t o d i f f e r e n c e i n t h e mean p a t t e r n l e g d i s t a n c e and a l t i t u d e was found have e s s e n t i a l l y t h e same c h a r a c t e r i s t i c s .

I n g e n e r a l S E H W a i y p l a n e s f l y c l o s e r t o t h e runt. y and higher than SELW a i r p l a n e s . TWIN a i r p l a n e s f l y h i g h e r and f u r t h e r from t h e runway than S E N and SELW, except on base and f i n a l where they have t r a n s i t i o n e d t o a lower mean a l t i t u d e .

Closure Rate Since a l l t r a f f i c g e n e r a l l y occupies t h e same a i r s p a c e i n t h e un- c o n t r o l l e d a i r t r a f f i c p a t t e r n environment, c l o s u r e rates between a i r p l a n e s whose p i l o t s f a i l t o see t h e o t h e r becomes an important c o n s i d e r a t i o n i n t h e development of any systems s o l u t i o n t o t h e mid-air c o l l i s i o n (MAC) problem. The average cumulative h o r i z o n t a l and v e r t i c a l c l o s u r e rates i n t h e t r a f f i c p a t t e r n were determined f o r G A I and HYD, f i g u r e 1 2 . The median c l o s u r e r a t e between a i r p l a n e s expected i n a t y p i c a l g e n e r a l a v i a t i o n uncontrolled t r a f f i c p a t t e r n is 18 knots h o r i z o n t a l l y and 1.3 m/sec (258 f t / m i n ) v e r t i c a l l y . Peak c l o s u r e rates i n a t y p i c a l g e n e r a l a v i a t i o n environment w i t h i n t h e p a t t e r n l e g s should not exceed 85 knots and 5.4 m/sec (1,068 f t / m i n ) more than 2% of t h e time. I f turbo-prop powered twin- engine a i r p l a n e s u s e t h e environment, such as t h e c a s e a t SBY, t h e average c l o s u r e rate i n t h e p a t t e r n l e g s w i l l be i n c r e a s e d . For SBY, t h e median h o r i z o n t a l c l o s u r e rate was found t o be approximately 45 knots and ex- ceeded 1 4 4 knots 2% of t h e t i m e - a s i g n i f i c a n t i n c r e a s e over t h e peak rates f o r HYD and G A I . V e r t i c a l c l o s u r e r a t e s a l s o increased t o a median of 1.9 mlsec (375 f t l m i n ) and exceeded 7 . 3 mlsec (1437 f t l m i n ) 2% of t h e time. The p o s s i b l e c l o s u r e r a t e s during and p r i o r t o pat,ern e n t r y a r e even higher and exceed 360 knots i n t h e SBY environment. Closure r a t e s determine how f a r i n advance of a MAC t h a t a warning m u s t be i s s u e d . To provide a 20-second warning time a t a 360 knot c l o s u r e r a t e would r e q u i r e i s s u i n g the warning when t h e a i r p l a n e s were separated by g r e a t e r thar. 2 n. m i . It is not considered unusual t o have s e v e r a l a i r p l a n e s with s e p a r a t i o n s of less than 2 n. m i . a t r e l a t i v e l y high c l o s u r e r a t e s i n a high d e n s i t y uncontrolled a i r p o r t t r a f f i c a r e a .

Separation Distance Another f a c t o r which may a f f e c t MAC systems performance and required accuracy is t h e normal s e p a r a t i o n d i s t a n c e s used by g e n e r a l a v i a t i o n p i l o t s i n t h e uncontrolled t r a f f i c p a t t e r n : I n r e f e r e n c e 8 , p i l o t s i n d i c a t e d they used an average of approximately 1 n . m i . s e p a r a t i o n i n t h e t r a f f i c p a t t e r n . The a c t u a l s e p a r a t i o n d i s t a n c e s measured a t a t y p i c a l u n c o n t r o l l e d a i r p o r t were g e n e r a l l y less than 1 n. m i . T h i s is i l l u s t r a t e d by f i g u r e 13 i n which a t y p i c a l s e p a r a t i o n t r a c k shows much l e s s s e p a r a t i o n t h a n 1 n. m i . I n f a c t , t h e minimum seDaration d i s t a n c e f o r a number of tracks was less t h a n 0 . 1 n. m i . during a portio.1 of t h e t r a c k . The c u a u l a t i v e d i s t r i b u t i o n s of t h e average s e p a r a t i o n d i s t a n c e and t h e minimum d i s t a n c e observed f o r each t r a c k a r e shown i n f i g u r e 14. The median average s e p a r a t i o n d i s t a n c e f o r each p a i r of a i r c r a f t t r a c k s was found t o b e 0.73 n. m i . ; however, a s i g n i f i c a n t percentage (16%) u s e d a n average s e p a r a t i o n of less t h a n 0.5 n. m i . ?he median minimum s e p a r a t i o n d i s t a n c e observed f o r each p a i r of t r a c k s w:.s found t o be 0.49 n. m i . arid 10% of t h e a i r c r a f t c l o s e d t o less than 0.7 n. m i . The s e p a r a t i o n d i s t a n c e s observed t l l u s t r a t e t h a t g e n e r a l a v i a t i o n - ) i l o t s o f t e n use s e p a r a t i o n s i n t h e u n c o n t r o l l e d t r a f f i c p a t t e r n t h a t are extremely c l o s e .

F i n a l Approach T r a j e c t o r i e s F i n a l approach t r a j e c t o r i e s , g e n e r a l l y , show c o n s i d e r a b l e v a r i a t i o n from s t a b i l i z e d , s t e a d y f l i g h t paths. P r o f i l e s of t h e f i n a l approach trajectories f o r t h e high-wing a i r p l a n e a t t h e long runway a r e presented i n f i g u r e 15. Included i n t h e f i g u r e are t h e median and t h e 5- t o 95- p e r c e n t i l e spread of t h e d a t a f o r t h e h e i g h t of the a i r p l a n e a t t h e t h r e s h o l d and t h e touchdown d i s t a n c e from t h e t h r e s h o l d . For r e f e r e n c e , 3 ' and 6 ' s l o p e s passing through t h ? median h e i g h t a t t h e t h r e s h o l d a r e included .

For both aArplanes a t both runways thg average f l i g h t p a t h angle ranged from 4.7 a t t h e long runway t 0 ~ 6 . 1 a t t h e s h o r t runway w i t h t o 14' during p o r t i o n s gf t h e i n d i v i d u a l f l i g h t p a t h s ranging from 1 approaches. The average f l i g h t path a n g l e was approximately 1 s t e e p e r a t t h e s h o r t runway than a t the long runway.

The median h e i g h t a t t h e threshold was lower f o r t h e low-wing a i r p l a n e thar? f o r t h e high-wing airplai.2 a t both runways. Howcver, both a t r p l a n e s were brought !n lower over t h e threshold a t t h e s h o r t runway t_ha!i a t t h e long runway, even though t h e average f l i g h t path angle was approximately 1 s t e e p e r .

The median touchdown d i s t a n c e was i n d i r e c t r e l a t i o n t o t h e median h e i g h t of t h e r e s p e c t i v e a i r p l a n e s a t t h e t h r e s h o l d . That is, the lower t h e median h e i g h t a t t h e t h r e s h o l d t h e c l ~ . -t.>r t h e median touchdown was t o t h e t h r e s h o l d . The median touchdown d i s t a n c e f o r both a i r p l a n e s a t b o t h runways was w i t h i n t h e first t h i r d of t h e runway, b u t w e l l beyond t h e runway d e s i g n a t i o n numbers j u s t past t h e t h r e s h o l d . The median touchdown from 10 percent t o 16 percent f o r both a i r p l a n e s a t both runways ranged of th, runway l e n g t h .

F i n a l Approach Airspeed The averag? f i n a l approach a i r s p e e d and t h e average f l a p d e f l e c t i o n measured a t 5-second i n t e r v a l s f o r t h e 60-second period p r i o r t o touchdown are presented i n f i g u r e 16 f o r t h e high-wing a i r p l a n e a t boch runways.

Also included i n the f i g u r e are r e f e r e n c e approach speeds and t h e measured s t a l l speeds of t h e a i r p l a n e a t t h e nominal test weight. The r e f e r e n c e approach speeds are i n t e r p o l a t e d v a l u e s of t h e manufacturer's recommended approach speeds using t h e average f l a p d e f l e c t i o n a t each t i m e period.

I n general, t h e p i l o t s flew t h e f i n a l approach with a n average speed considerably f a s t e r than t h e r e f e r e n c e speed. I n f a c t , t h e average approach speeds were more than 5 knots i n excess of t h e r e f e r e n c e speeds u n t i l w i t h i n 15 seconds or less of t h e touchdown, a s i n d i c a t e d by t h e s o l i d symbols i n f i g u r e 16. The exception t o t h i s result w a s t h e low- w i n g a i r p l a n e a t t h e s h o r t runway i n which case t h e average speed was only s l i g h t l y i n excess of t h e r e f e r e n c e speed f o r ;he f i n a l 40 seconds p r i o r t o touchdown.

Another p o i n t of i n t e r e s t shown by t h e d a t a is t h a t t h e f i n a l approach opzerjs a t t h e s h o r t runway were slower than t h o s e a t t h e long runway f o r both a i r p l a n e s . This c o r r e l a t e s d i r e c t l y with t h e l a r g a average f l a p d e i l e c t i o n used a t t h e s h o r t runway. However, t h e r e d u c t i o n i n average approach speed (6 t o 12 knots) w a s much g r e a t e r than t h e d i f f e r e n c e i n t h e r e f e r e n c e approach speeds ( 1 t o 2 k n o t s ) . This d i f f e r e n c e would i n d i c a t e t h a t t h e p i l o t s were concerned about t h e runway l e n g t h and were paying c l o s e r a t t e n t i o n t o a i r s p e e d during t h e approaches t o t h e s h o r t runway t o a s s u r e landings with a comfortable margin between t h e stopping p o i n t and t h e end of t h e runway. Based on t h e manufacturer's published landing d i s t a n c e s f o r t h e a i r p l a n e s , t h e designated s h o r t runway w 2 s n o t , i n f a c t , a "short runway" r e q u i r i n g maximum performance from e i t h e r a i r p l a n e or p i l o t t o achieve a normal landing i n t h e a v a i l a b l e d i s t a n c e .

Touchdown Airspeed Cumulative d i s t r i b u t i o n of e i r s p e e d a t touchdown f o r t h e high-wing Included i n t h e a i r o l a n e a t both runways is presented in f i g u r e 1 7 .

f i g u r e are t h e measured s t a l l speeds or' t h e a i r p l a n e a t t h e nominal test weight and t h e r e f e r e n c e approach speeds based on t h e f l a p s e t t i n g s f o r t h e l a s t 10 seconds of t h e approaches.

The d a t a g e n e r a l l y show t h a t t h e p i l o t s landed t h e a i r p l a n e with speeds considerably i n excess of t h e s t a l l a i r s p e e d ; t h i s is most probably a d i r e c t r e s u l t of t h e excesa.ive a i r s p e e d used during t h e f i n a l approach.

The median touchdown speed ranged from 13 percent t o 48 percent above t h e measured flaps-up s t a l l speed, and l e s s than 6 percent of t h e landings were w i t h i n t h e s t a l l speed range. Except f o r t h e low-wing a i r p l a n e a t t h e s h o r t runway, a r a t h e r high percentage of t h e landings were made i n excess of t h e r e f e r e n c e approach speeds. The touchdown speeds a t t h e s h o r t runway were s i g n i f i c a n t l y less than those a t t h e long runway by approximately t h e same amount as t h e d i f f e r e n c e i n t h e f i n a l approach speeds between runways.

Touchdown P i t c h A t t i t u d e Associated w i t h t h e high touchdown speeOs were p i t c h a t t i t u d e s t h a t were r e l a t i v e l y f l a t f o r both a i r p l a n e s a t both runways. The cumulative d i s t r i b u t i o n s of p i t c h a t t i t u d e a t touchdown f o r t h e high-wing a i r p l a n e are presented i n f i g u r e 18. Included i n t h e f i g u r e is a l i n e i n d i c a t i n g t h e i n - f l i g h t three-point touchdown a t t i t u d e which s e p a r a t e s t h e r e g i o n s of nose-wheel and main-wheel landing a t t i t u d e s . I n g e n e r a l , t h e touchdown p i t c h a t t i t u d e s show l i t t l e t o no d i f f e r e n c e w i t h r e s p e c t t o runways.

The d a t a show t h a t t h e p i t c h a t t i t u d e s a t touchdown were r e l a t i v e l y f l a t f o r both a i r p l a n e s a t both runways. The median touchdown a t t i t u d e ranged from only 1.4O t o 2 . 6 ' above t h e t h r e e - p o i n t a t t i t u d e (pitch-up).

A s i g n i f i c a n t percentage of t h e l a n d i n g s w a s made i n which t h e nose wheel contacted t h e runway b e f o r e t h e main wheels. Approximately 1 2 p e r c e n t of t h e l a n d i n g s were nose wheel f i r s t , except f o r t h e low-wing a i r p l a n e a t t h e s h o r t runway where t h e percentage was 22 p e r c e n t . Nose-wheel l a n d i n g s are almost i n v a r i a b l y a d i r e c t r e s u l t of allowing a n a i r p l a n e t o touch down with an e x c e s s i v e l y high a i r s p e e d and c e r t a i n l y p r e s e n t t h e p o t e n t i a l f o r a landing a c c i d e n t due t o nose wheel c o l l a p s e , porpoising of a i r p l a n e , or u n s t a b l e a i r p l a n e motions r e f e r r e d t o as wheel-barrowing.

Mid-Air C o l l i s i o n Simulation Using t h e approach d a t a presented i n t h i s paper a math model capable of s i m u l a t i n g uncontrolled a i r t r a f f i c p a t t e r n s h a s been developed. MAC s i m u l a t i o n s which d u p l i c a t e t h e e x i s t i n g environment can provide a b a s e l i n e f o r e v a l u a t i n g t h e e f f e c t of changing t h e u n c o n t r o l l e d p a t t e r v concept o r t h e e f f e c t o r improvements i n g e n e r a l a v i a t i o n p i l o t i n g procedure. The technique u t i l i z e d is i l l u s t r a t e d i n f i g u r e 19 which shows t h e p o s i t i o n t i m e h i s t o r i e s of two a i r p l a n e s i n a t y p i c a l approach procedure t h a t are t i m e normalized t o have a MAC on f i n a l approach. The view a n g l e from both a i r p l a n e s t o t h e o t h e r w a s computed based on t h e i r heading, bank angle, and r e l a t i v e p o s i t i o n s . A t i m e h i s t o r y of t h i s d a t a is p l o t t e d on t h e view envelope of each a i r p l a n e , f i g u r e 20, and t h e p e r c e n t of t i m e each a i r p l a n e is v i s i b l e t o t h e o t h e r p i l o t determined, r e f e r e n c e 10.

The result, f i g u r e 21, i l l u s t r a t e s t h e cumulative p e r c e n t of t i m e each p i l o t had t o d e t e c t t h e o t h e r from a s e p a r a t i o n d i s t a n c e of approximately 3 n. m i . The c a s e shown is r e p r e s e n t a t i v e of normal g e n e r a l a v i a t i o n approaches, y e t , n e i t h e r p i l o t could have seen t h e h e r a i r p l a n e approxi- mately 65 p e r c e n t of h i s approach time. Using t h i s If technique t h e cumulative p r o b a b i l i t y of a MAC can be estimated by i n c l u d i n g t h e p r o b a b i l i t y of each pilot looking and the probability of seeing when he looks as a function of the separation distance. By simulating thousands of such MAC'S in this manner and defining the baseline for the existing uncontrolled traffic pattern environment, the relative improvements that may be achieved through changes in piloting procedure or by new pattern concepts can be determined. Typical pattern concepts under consideration are shown in figure 22. General aviation pilots have indicated, reference 8 , that approximately 44 percent preferred the standard left-hand pattern and 30 percent preferred the proposed pattern shown.

Systems Studies The uncontrolled air traffic studies indicate that new piloting and/or pattern concepts may not adequately reduce the MAC hazard at high density uncontrolled airports. Based on the traffic characteristics observed a systems definition study is in progress to determine the feasibility of a low-cost Automated Pilot Advisory System ( P A S ) , re- ference 11, for high density, uncontrolled airports. The system concept, figure 23, under evaluation would utilize a small skin tracking radar, microprocessors, weather sensors, and a VHF transmitter. The system functions identified for evaluation are: 1. Broadcast an airport advisory voice message once every two minutes which specifies the active runway, surface winds, barometric pressure, and temperature.

2. Broadcast. an air traffic advisory voice message every two minutes which specifies the location of all traffic within 3 n.

mi. of the airport.

3. Broadcast a mid-air collision advisory voice message whenever two airplanes exceed a 15-second Modified Tau Criteria, re- ference 12.

4 . Provide the FBO with runway select and override functions and the capability to record limited cautionary messages to be i-nciuded in airport advisory message.

5. Provide for remote access of system information, via telephone.

Pulse, pulse-doppler, and doppler radar systems are under evaluation for this application. Low-cost X-band radars which appear suitable for this application are readily available as marine and airborne weather radars.

The computer would provide the essential system logic and control functions. These include radar data processing, clutter rejection, track-while-scan, weather data processing, logic and generation of pre- stored advisory word message formats, power failure auto-restart function, : . : B O control. functions and system self checks.

Whenever the various computer logic conditions are met, a VOiCC message i n a standard word sequence would be generated. Computer software will interlace proper key words into the standard format to complete the advisory nessage. Pre-recorded digital message sequences and vocoder voice r;ythesis techniques are under evaluation for this system. Typical message sequences with underlined key words follow:

AIRPORT ADVISORY - HYDE - ACTIVE RUNWAY - THREE-ONE - RIGHT HAND PATTERN -

W I N D - TWO-ONE-FIVE AT SIX KNOTS - ALTIMETER -- THREE ZERO POINT -- ZERO FOUR -

-

TEMPERATURE IS - TEN DEGREES.

or

- TRAFFIC ADVISORY - HYDE - AIRCRAFT AWAITING DEPARTURE - AIRCRAFT ON

FINAL - TWO AIRCRAFT DOWNWIND - ARRIVING AIRCRAFT THREE MILES - NORTHEAST ---

- -

DEPARTING AIRCRAFT - ONE MILE SOUTHEAST.

An experimental PAS will be configured to evaluate the various system performance options, message formats, and pilot reaction to system utility.

CONCLUING REYARKS The characteristics of general aviation piloting procedures during approach and lending have been documented. Data presented illustrate the variability with which the uncontrolled air traffic patterns, and the approach and landing maneuvers are performed. Results confirm that pattern enti-y locaticii and procedure are often inconsistent with the local o r accepted standard pattern. The uncontrolled traffic pattern legs are UF t o 1 n. mi. wide for typical general aviation airports and may exceed 2 r . . mi. in width in environments including high performance twin-engine airplanes. Significant variation from the established pattern altitude, + 75 m ( 2 4 6 ft), is not unusual. At airports where a crosswind pattern leg is utilized, specific procedures are needed for arrival and touch-and-go traffic. Departure traffic should abide by the recommendations of FAA Advisory Circular AC No. 90-66. Systems to prevent ?lAC at high density uncontrolled airports must cope with very low and high closure rates and noriaal VFR traffic separation distances of 0.1 n. mi. or less.

The average final approach airspeeds were generally higher than recommended which produced significant floating during the landing flare, average touchdown speeds well above airplane stall speed and landing :,itch attitudes that were generally flat or nose-low. On the average, pilots used higher flap deployment angles, steeper approaches, less speed and achieved landings closer to threshold on the short runway when compared to the long runway approaches.

The t i r e available f o r p i l o t s t o see-and-avoid a HAC with other a i r p l a n e s i n t h e uncontrolled p a t t e r n environment m y be r e l a t i v e l y short. Xanue*vers and vision view f i e l d r e s t r i c t i o n s c r e a t e t h i s s i t u a t i o n ; however, the a b i l i t y t o d e t e c t other airplanes a t greater than 1 n. r i . , t h e percentage of t i m e p i l o t s spend looking f o r other airplanes, a d rapid closure rates o f t e n involved are f a c t o r s which increase t h e M C hazard. The P i l o t Advisory System concept may provide p i l o t s with g r e a t e r a b i l i t y t o locate and avoid conflicting t r a f f i c , i f law-cost system f e a s i b i l i t y is demonstrated.

REFERENCES 1 . Anon.: Aircraft Accident Reports, Brief Format. National Transportation Safety Board. NTSB-BA-71-3, 1970.

2 . Mid-Air Collisions in U . S . Civil Aviation 1969 - 1970. Special

Study, National Transportation Safety Board, Report No. NTSB-AAS- 72-6, Washington, D . C. June 7, 1972.

3. Near Mid-Air Collision Report of 1968. Department of Transportation, Federal Aviation Administration, Air Traffic and Flight Standards Technical Report, prepared by NMAC Study Group, July 15, 1969.

4 . Mid-Air Collisions in U. S . Civil Aviation - 1968 - A Special

Accident Prevention Study. National Transportation Safety Board, Washington, D. C., July 1969.

5. Parker, L. C.: General Aviation Air Traffic Pattern Safety Analysis.

NASA TM-X-6955, The System Safety Society Symposium, July 17, 1973.

O'Bryan, Thomas C.; Goode, Maxwell W.; and Harris, Randall L . : A 6 .

Study of Light Airplane Pilot Landing Performance. Society of Automotive Engineers, Inc. 740350, 1974.

7 . Anon. : Jeppesen Private Pilot Course. Times Mirror 1971.

Parker, Loyd C . : Pilot Preference and Procedures at Uncontrolled 8.

Airports. NASA TN D-7928, 1975.

9. Anon.: Recommended Standard Traffic Patterns for Airline Operations at Uncontrolled Airports. Department of Transportation, Federal Aviation Agency, AC 90-66, 1975.

10 * Bashir, J. and Singh, R. P . . Aircraft Cockpit Vision Math Model.

NASA CR-141406, July 1975.

Parker, Loyd C . : NASA Study of An Automated Pilot Advisory System.

11.

760460, Society of Automotive Engineers, April 1976.

12. Britt, C. L.: A Look at Alarm Rates in Collision Warning Systems.

Trans. of the 16th Annual Air Safety Forum, Airlines Pilots Assc- ciation, July 1969.

+- 3NM MEOIAN IC111 TRAFFIC PERCENTAGE

m 50%

D 20% c3 4 % (a) Salisbury.

3 1 '5- s.

TRAFFIC PEKfNN7AGE rn SO 7.

e=!l20%

m 4%

2+ (b) Hyde.

Figure 7 . - Traffic pattern l e g distance distribution.

l a!

o r I I 1 r' 0 1 1 3 m a OISVANCf (a) Downwind leg.

W O 0 0 5 -

9. -

0 s -

7s -

CUMULI1 I V .

D I S I R I ~ U I I O N

50 -

Y5 -

5 - I - O 5- 0 1 1 1 ' 1 (b) Base leg.

Figure 8.- Cumulative distribution of pattern l e g distance.

I I I J 0 0 I S I A N C I (c) Final leg.

Figure 8 . - Concluded.

I10 9 9 -

81 -

1 s - CUMULAIIY 1 OI51RIDU1ION so- 0 M 1 O - L I s 1 (1 C A I - 1 1 V 1

0 0.1 - l I O M 1

?S-

3 I D 1 - L t F I

5- I ?

O ! I, < t 1 1 1 I wo 500 100 900 1100 1300 n o 0 (I h l 1 I 1UOf (a) Downwind l e g .

*

99 -

9s -

7s -

t U Y U L A l I Y @ DIS1 ll #Ut ION M-

I5 -

- M Y O - l I I 1

r . 0 A -1111 5 0.1-RIGW I - **J 5 l I -LEI) I, I I 1 1 I 1 O I 1 4 0 IO0 ?OO 300 400 450 m 7 1 1 I I I I 1

f I loo 300 so0 TOO 900 I I O 0 0 0 0 IS00 41

AllllU01 (b) Base l e g .

Figure 9.- Cumulative distribution of pattern l e g a l t i t u d e .

?5 -

C U M U L I 1t V t O I S I I I W I I O N 50- 25- 1-I d 6 Of I I 1 1 0 50 I50 2 5 0 300 m i I I f I‘ zuo 4 0 0 b o 0 860 1000 9 1 4 L I I I U O I (c) Final leg.

Figure 9 . - Concluded.

1 Y P I C A 1 D E P A R T U R E P A T M l W J N SJNGLE ENC 2100-- 1800-- 1500.- A L T I T U D E 1200.- 900.- 600.- 300.- b D I S T A N C E Figure 10. - Crosswind leg t r a f f i c percentage and typical departure pathe.

1 .

-Ala *IC

. . . .-

--saw

- -4WlN

(a) Nean distance.

ALTITUDE (b) Mean altitude.

Figure 11.- Comparison of mean distance and altitude by type of aircraft at SBY.

(a) Horizontal closure rate.

(b) Vertical clcsure rate.

Figure 12.- Expected horizontal and vertical closure rates.

Figure 1 3 . - Aircraft position - time separation tracks.

Figure 1 4 . - Cumulative distribution of average and minimum separation distance.

m RUNWAY END

n

I I I I I loo.

I HEIGHT I I ABOVE MEDIAN HEIGHT I RUMWAY ~ I I . . . .

0 -

-300 -200 -100 0 100 200 300 400 50 600 1uw) 1600m

I I I I I I I I d

-800 -400 0 . 400 800 1200 1600 m 5 O O o n

THRESHOLD 01 STANCE Figure 15.- Final approach trajectories for high-uing airplane on long m a y .

0 LONG RUNWAY S SHORT RWWAY ---e- LONG RUNWAY REFEREME APPROACH SPEED ---SHORT RUMWAY REFERENCE 60: I vSTALL SPEED RANGE 2 0 - 1 1 1 1 I 6 b 5 0 4 0 3 0 2 0 1 0 b TIM BEFORE TOUCHDOWN. S S Figure 16.- Final approach airspeed and flap deflection for high-wing airplane.

L L - _--_- 1 ___-_ ---A A I - M do 4 60 a 80 AIRSPEED AI IOUCHDWN. knots Figure 1 7 . - Cumulative distribution of airspeed at touchdown for high-wing airplane.

0 LONG RUNWAY 0 SHORT RUNWAY 2 0 2 4 6 8 1 0 1 2 1 4 PITCH ATTITUDE A T TOUCHDOWN. d q Figure 18.- Cumulative distribution of pitch attitude at touchdown f o r high-wing airplane.

500- 100- I TIME T O THPESMOLD (seconds) NM * 1 .o -0.5 .o.o HASH W Y S ARE SECONDS TO MESHOLD AT 10 SECOW INTERVALS -0.5 .-1.o NI# -3.0 -2.0 -1 .o 0 . 0 Figure 1 9 . - ?:id-air collision position and altitude time history.

'- . .-.

i f f ' - 1 ..- Figure 20.- Aircraft view envelopes.

% I Y *-O-u- -(t--o 1>-43- U - - 0 u) C U W U L A I l U t Ptrccnr Of U-- 1IYt U l s l e l f 10 6 1 0 -..

I I 0 220 2Qo 180 160 I10 riwc IO r n 1 o - m C O L L I S I O N Figure 21.- Separaticn distance and cumulative percent of time v i s i b l e as a function of time to PAC.

2 . Proposed 1. Standard

L e f t =

Right fl

A .

3. S t r a i g h t - i n Left L27 R i g h t

> - + +

5 . 6 . I n s t . Procedure

Left L7 Left n

R i g h t Right

'I

Figure 22.- Uncontrolled a i r traffic pattern concepts.

0 - 60' COVERAGE 6 V BAAO PRESS COMPUTER RADAR A/C TRACK RUNWAY SET LOGIC MESSAGE ___-__-- STORE/PLAY Figure 23.- Conceptual p i l o t advisory system.