AAIB Bulletin: 6/2006

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60 © Crown copyrght 2006 AAIB Bulletin: 6/2006 N421CA EW/C2005/09/11 ACCIDENT Aircraft Type and Registration: Cessna 421C Golden Eagle, N421CA No & Type of Engines: 2 Continental TCM GTS10 piston engines Year of Manufacture: 976 Date & Time (UTC): 30 September 2005 at 1817 hrs Location: Northrepps Airfield, Cromer, Norfolk Type of Flight: Prvate Persons on Board: Crew -  Passengers - 2 Injuries: Crew - None Passengers - None Nature of Damage: Substantial to landing gear, engines, wings, and fuselage Commander’s Licence: Prvate Plot’s Lcence Commander’s Age: 44 years Commander’s Flying Experience: 2,475 hours (of whch 255 were on type) Last 90 days - 82 hours Last 28 days - 35 hours Information Source: AAIB Feld Investgaton and vdeo evdence provded by a member of the public History of flight Northrepps Airfield has a single grass runway, orientated 18/36, and 1617 ft (493 m) long, wth a down slope of 1.8% on Runway 18. On the day of the accident, the short grass was wet and an aftercast ndcated that the wind at Northrepps was from approximately 210º at 10 to 13 kt. The pilot first flew an approach to Runway 18 and touched down close to the threshold; he subsequently reported that, lookng at the slope of the runway ahead of him, he decided to go around and re-position for a landng on Runway 36, to take advantage of the up-slope on that runway. Footnote  In ths report, all dstances are n feet, snce the arcraft manufacturer’s Flight Manual data is presented in feet. The plot stated that, durng the approach to Runway 8, he had assessed that the brakng effect of the wnd would be insignificant in comparison to the braking effect that would be afforded by the uphll slope when landng on Runway 36. The pilot recalled seeing a “shortened” and “non-standard” windsock mounted on a caravan adjacent to the Runway 18 threshold, but he did not beleve that t could be reled upon for an accurate wnd strength determination. He did not recall having seen the airfield’s other, larger, windsock. The approach for a short field landing on Runway 36 was normal and the pilot closed the throttles just before 6 © Crown copyrght 2006 AAIB Bulletin: 6/2006 N421CA EW/C2005/09/11 the threshold. The arcraft touched down close to the threshold, and the pilot immediately retracted the flaps. The plot reported that he had lost two thrds of hs touchdown speed by about the mid-point of the runway, and that the brakng was wthn hs expectatons. He subsequently stated that he “seemed to get to a point… when I realsed that I was effectvely gettng no braking at all from the wheels and the uphill slope had petered away”; he then experienced a sensation which he described as being similar to aquaplaning, with all braking authority seemingly lost. The arcraft contnued along the runway, crossed the grassed overshoot area, ran over an earth bank beyond the end of the runway and came to rest on a public road just north of this bank. The pilot shut the aircraft down and all three occupants vacated the arcraft wthout difficulty. Video evidence A member of the public recorded portions of the flight including both the touchdown and go-around on Runway 8 and the approach and landng on Runway 36, from a position adjacent to the northern end of the runway. The moment of touchdown on Runway 36 was not recorded, as the southern end of the runway was obscured from view by the slope of the terrain. Background to the flight The plot had bought the arcraft two weeks pror to the accident, and had flown 17 hours in the aircraft in that time. Previously, he had flown over two hundred hours in an aircraft of the same type, ceasing that flying some two and a half years before the accdent. He had not receved any refresher tranng on the arcraft. Although the plot had consderable experence of operating from ‘short’ grass strips including the arcraft’s base (whch has a grass runway 2,532 ft long), he had not flown to Northrepps before. He had however, consulted a proprietary flight guide and made telephone enquiries from the airfield operator and had decided that the operaton nto Northrepps was feasble. He dd not inspect the aircraft flight manual to determine landing dstance or ground roll requred, but reported that he considered that it would be “easily within (the aircraft’s) capabltes of landng wth the arrestng force of grass and up hill” n the dstance avalable at Northrepps. Performance information The arcraft Flght Manual, approved by the FAA, provides information on landing distance and ground roll, presented in tabular form, and for various weights, temperatures, and pressure altitudes. To achieve the given landing performance, the Flight Manual states that the throttles should be fully closed at 50 ft above the runway and the arcraft should be fully stalled at touchdown. Given a temperature of +20ºC, in still air, at a weight of 6,000 lb, and at an airfield at mean sea level, the quoted landng dstance was 2,070 ft, and the assocated ground roll was 500 ft. The aircraft Flight Manual did not provide a means of allowing for runway slope, but CAA Safety Sense Leaflet 7C suggests that a 2% runway down-slope increases landing distance by 10%, and states that ‘Effect on ground run/roll will be greater’. The Leaflet does not suggest a reducton n dstance n the case of an upslope. However, n the followng calculatons ths factor has been appled n the reverse sense (although t should be emphasised that this does not imply that this would provde an acceptable bass for the safe conduct 62 © Crown copyrght 2006 AAIB Bulletin: 6/2006 N421CA EW/C2005/09/11 of operatons). The arcraft Flght Manual stated that the distances should be reduced by 3% per 4 kt of headwind and increased by 8% per 3 kt of tailwind. The Flight Manual did not offer a means of allowing for a runway