Report IN-023/2008

been removed from the aircraft, overhauled as required by the calendar limits, and then re-installed. Once the scheduled maintenance tasks were complete, and so as to renew the Airworthiness Certificate, a check flight had to be completed. The permit to flight had been requested and granted, on 17-06-2008. It was valid for ten days and subject to the following conditions: no passengers, no payload, minimum crew and VMC. It was this permit that was used to conduct the flight on which the incident took place. 1.3.6. Technical maintenance documentation According to the requirements of the aircraft’s approved maintenance program, it must be maintained as per the latest Cessna 177 RG Maintenance Manual and Parts Catalog, and the engine as per the Avco Lycoming IO-360 Maintenance Manual. The Maintenance Manual applicable to the aircraft was Cessna reference document D991-3-13, titled “Cardinal RG Series 1971 thru 1975 Service Manual”, dated 01-09- 1972, Revision 3, dated 01-09-1974. On the date of the incident, there were six temporary revisions to this manual issued by the manufacturer, of which only the first was included in the manual. The rest had been distributed separately, and were: 2, dated 03-10-1994; 3, dated 07-01-2000; 4, dated 07-10-2002; 5, dated 11-07-2005; and 6, dated 15-01-2008. 195 2 In this case, the time interval between engine overhauls was 2,000 h. 3 Since the propeller was of the variable pitch type, this note applies equally to the governor. Report IN-023/2008 The installation of the propeller governor is described in Section 13, Sub-section 13.1 of said manual, which was modified by Temporary Revision 5 to the manual. Appendix A to this report includes the pages from the Maintenance Manual relevant to the governor and the text of Temporary Revision no. 5 to the Manual. As regards the installation, Section 13-11 of the Manual, “INSTALLATION”, Item c, states: “c. Install a new mounting gasket on the mounting studs. Install gasket with raised surface of the gasket screen toward the governor.” In Temporary Revision no. 5, the text in this section is modified to read: “c. Install new Lycoming part number 72053 Gasket on the mounting studs. Install a Lycoming LW-12347 Plate over the 72053 Gasket and a MS9144-01 Gasket over the LW-12347 Plate. Install gasket with raised surface toward the governor. Refer to Lycoming Service Instruction 1438 or latest revision.” Appendix B to this report is the Lycoming Service Instruction (SI) no. 1438A, dated 09- 12-2005, which details the installation of the propeller governor on the engine using two gaskets and a plate between them. This installation is required on certain propeller governors to eliminate the possibility of oil leakage between the governor and the engine accessory housing. Appendix C to this report is the Federal Aviation Administration’s (FAA) Special Airworthiness Information Bulletin (SAIB) NE-06-08, dated 09-11-2005 and amended on 14-11-2005, which lists the known engine models, and the airplanes on which they are installed, affected by Lycoming Service Instruction no. 1438A. The list includes the Lycoming IO-360-A1B6D engine installed on Cessna 177 RG Cardinal airplanes. 1.4. Inspection of airplane after incident The airplane was taken to the hangar at Cuatro Vientos airport, where the structural damage was verified to have been limited to that noted during the field inspection and confirmed to be, in general, minor. The external inspection of the power plant confirmed the presence of an oil leak where the governor is coupled to the engine. Additionally, the engine could not be turned and the forward crankshaft retainer had shifted from its housing. A 4-cm hole was also found in the main engine crankcase, located between the no. 4 cylinder lifters, and due to which the camshaft was visible. The hole was apparently made by the impact from an unidentified engine component. As a result of the above, it was decided to inspect each component separately. 196 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 1.4.1. Propeller inspection The assembly was removed from the group without any difficulty once the blades, whose tips were scratched and bent backwards (see Fig. 3) were confirmed to be in the lower pitch position. The damage to the blades showed that the aircraft had contacted the ground without thrust and at low rpm’s. The blades and hub components were then removed. No appreciable damage was found in any of these parts. 1.4.2. Propeller pitch control (governor) and findings from inspection On the engine type installed on the aircraft, the propeller governor is installed in the fitting at the lower left of the engine accessory housing. The governor is a device that varies the pitch of the propeller blades so as to maintain the rotation speed selected by the pilot. The variation is achieved by applying the pressure generated by the governor’s own pump to the pitch actuator, which is located in the propeller hub. The pump is supplied by engine oil, which it takes directly from the crankcase before it flows through the filter. On the type of propeller installed on the aircraft, the pitch increases to minimum rpm’s by increasing the pitch actuator pressure when the pilot moves the control to higher positions, and decreases to maximum rpm’s by the effect of the centrifugal force of the blades when the pilot reduces the pressure by moving the control downward. The inspection of the governor confirmed the visual indications of the leak mentioned earlier. There was no damage to either the mechanical linkage from the cockpit control to the governor nor to the line that carries oil from the governor to the pitch actuator in the propeller hub. This line was found to contain only a few drops of a dense, gray- colored oil. The small amount of oil in the line indicated that the oil flow had been cut off prior to the stoppage of the propeller. The governor was removed from its vent in the engine accessory housing without any problems. It was confirmed that there was only one MS 9144-01 type gasket in the engine coupling, as required by the aircraft’s Service Manual. There was a large amount of metal shavings in the gasket screen. The exact cause of the oil leak at the engine coupling could not be determined. The likely possibilities include a defect in the gasket, either pre-existing or caused during the installation, improper tightening of the bolts that attach the governor to the engine, either due to the wrong applied torque or, because of a faulty installation, the grooved 197 Report IN-023/2008 end of the governor was in contact with the depth of the engine drive gear such that the governor body could not be tightened against the engine. The leak could also have been caused by a combination of these factors. The governor itself was inspected at the workshop of the specialized company that had done the overhaul before the flight and using the same test bench. The resistance to rotation found at the start of the inspection disappeared when the metallic particles, both magnetic and non-magnetic, that had collected at the oil inlet and outlet ports were removed. Functional tests were then performed on the test bench and resulted in stable operation within tolerances. The governor was removed and its internal components found to be in good overall conditions. There was only some localized wear on the non-moving parts caused by friction with rotating parts. In light of the results of the inspection, it was concluded that even though the oil leak had affected its operation, the governor had not malfunctioned. 1.4.3. Engine inspection When the engine was disassembled, a large amount of metallic, both magnetic and non-magnetic, shavings were found in the lower crankcase (Fig. 4) and greasing ports, and especially in the filter mesh at the suction to the engine oil pump. When the inside of this pump was inspected, its components were found to be in good condition, with only minor wear caused by friction between the gear teeth and the housing. The pump did not show any signs of having been run without oil. The cylinders were then disassembled from the main crankcase. The connecting rods on the nos. 2, 3 and 4 cylinders had detached from the crankshaft and showed signs of severe overheating, as evidenced by the flow of material in a longitudinal direction, especially in the no. 2 cylinder (Fig. 5). Some of the crankshaft bearings had also fractured and exited the race, causing scorching of the journal (Fig. 6). The damage to the main components increased with their distance from the oil pump. The no. 1 cylinder connecting rod remained attached to the crankshaft and its bearings; though they also showed signs of a lack of grease, they were not scorched. 198 Addenda Bulletin 4/2011 Figure 4. Metal particles and shavings in the crankcase Addenda Bulletin 4/2011 Report IN-023/2008 Figure 5. No. 2, cylinder, partly disassembled, Figure 6. Scorched crankshaft journal and showing broken connecting rod loose metallic debris The engine did not show any of the typical signs of seizing, such as static fractures of connecting rods and cylinders without any apparent deformations. In this case, considerable plastic deformation was found, caused by pulling in excess of the material’s creep load at high temperature over a period of time, typically resulting from operating the engine at high rpm’s, even above the maximum allowed (overspeed) with increasingly insufficient lubrication. In general, the engine mount bearings were in good condition and had traces of lubricating oil. There was much less oil found inside the engine than should have been present under normal conditions. In summary, the damage found was consistent with an engine operated at high rpm’s, possibly above the overspeed limit, in combination with a loss of oil that impeded its proper lubrication and resulted in excessive heating of the engine’s moving parts. The disassembly of the engine’s remaining components and accessories did not reveal the presence of other damage or provide additional information. 1.5. Pilot’s statement During the investigation into the incident, the pilot provided a report that details, among other things, the history of the flight, a description of the flight and some personal conclusions. As described in this report, the airplane took off at approximately 13:30 (local time) from runway 10 at Madrid-Cuatro Vientos Airport. The magneto, regulator, flight controls and other typical tests had been performed satisfactorily. Following the takeoff circuit, the pilot reduced engine speed and adjusted the altitude to 3,000 ft, departing the CTR circuit via point W. 199 Report IN-023/2008 He then climbed to 4,000 ft and, after just five minutes of flight, at a distance of 4.5 km west of Villaviciosa de Odon, detected a loss of thrust and increased engine rpm’s above 2,800, in excess of the maximum allowed. When he attempted to lower the rpm’s, the pilot noted that the propeller pitch control was not responding, after which he proceeded to turn toward the field while decreasing power to idle in an effort to limit engine damage. He also reported his position and status to ATC. The pilot then attempted to glide back to the airport, but upon noticing that the success of this operation was not guaranteed, he applied moderate thrust to obtain more power from the engine. Doing this caused the engine rpm’s to climb above 2,800 once again, resulting in strong vibrations that caused the cover on the control panel to fall and smoke that smelled of oil to enter the cockpit. Given the situation, the pilot decided to execute an emergency landing with the landing gear up, since he could not ascertain the topography of the wheat field on which he had decided to land. Prior to the landing, which was controlled, he shut off the fuel, contact and battery. As already noted, the aircraft traveled some 70 m over the terrain and stopped after turning some 60° with respect to the landing roll. The pilot left the aircraft in the event a fire broke out. He returned later after the situation was under control to inform ATC of his position. A helicopter from the Traffic Authority reported to the site within ten minutes. 1.6. Additional information 1.6.1. Similar incidents in the NTSB database A check of the United States National Transportation Safety Board (NTSB) database revealed two similar events, references LAX96LA270 and SEA07LA172, which took place on 13-07-1996 and 18-06-2006, respectively, and involved CESSNA 177 RG aircraft, registrations N52185 and N2144Q. Both flights had taken place immediately after installing the propeller governor. In the first case the governor had been removed to repair a malfunction, and in the second, for an overhaul. The flights lasted 1:40 and 1:10 h, respectively. The investigation into these events, which did not result in any injuries to persons, revealed that in both cases, the governor had been coupled to the engine using a single MS9144-01 gasket and that oil had leaked through this coupling. In both cases the leak caused a loss of oil pressure in the propeller governor, with the ensuing positioning of the blades in the fine pitch position and a loss of thrust, along with a lack of lubrication in the engine, which led to the overheating of the connecting rod sleeves and of the connecting rods themselves, especially near the crankshaft. This resulted in the plastic deformation and eventual fracture of some of these components. 200 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 As detailed in the relevant NTSB reports, the loss of oil pressure in the propeller governor and the lack of engine lubrication was caused in both cases by an oil leak at the propeller governor-engine coupling. The oil leak had resulted because only a single MS9144-01 gasket had been installed instead of a Lycoming 72053 gasket, a Lycoming LW12347 plate and then a MS9144-01 gasket on top. 1.6.2. Installation of the propeller governor on this aircraft The Authorized Maintenance Center (AMC) where the airplane’s propeller governor had been removed and then re-installed had the applicable maintenance documentation, which it kept updated via an electronic CD-ROM subscription (Avantext TechPubs CD). As part of the investigation, it was noted that the applicable edition of said CD-ROM (with the applicable updates from April to June 2008) included the Maintenance Manual, reference D991-3-13, titled “Cardinal RG series 1971 thru 1975 Service Manual”, dated 01-09-1972, Revision 3, dated 01-09 1974, which included Temporary Revision 1, in addition to Temporary Revisions 2, dated 03-10-1994, 3, dated 07-01- 2000, and 4, dated 07-10-2002 By the date of the incident, the AMC had already received the CD-ROM with the updates applicable for the next quarter, which included Temporary Revision 6, dated 15- 01-2008, but did not include Revision 5 or make any reference to it. The Maintenance Manual applicable to more modern versions of the same aircraft type, Cessna reference document D2009-4-13, titled “Cardinal RG Series 1976 thru 1978 Service Manual”, dated 02-10-1995, discussed the installation of the propeller governor using the same terms as in D991-3-13, and had been modified via Temporary Revision 6, dated 01-05-1997. When the airplane manufacturer was questioned about the applicable manuals, investigators were referenced to the on-line distribution of said manuals, which was accessed on 14-01-2009 and found to be identical to the CD-ROM edition. Specifically, it included Temporary Revisions nos. 2, 3, 4 and 6 to reference manual D991-3-13, but it did not include or make any reference to no. 5. When the manufacturer was questioned about this, it submitted the Temporary Revision no. 5, dated 11-07-2005, included in Appendix A, which has a note stating that the revision “will be incorporated to the Manual at a later date”. It was then that the existence of this temporary revision was confirmed and verified to be similar to revision no. 6 of reference manual D2009-4-13. The current version of the Maintenance Manual, reference D991-3-13, included in the electronic CD-ROM version includes Temporary Revision no. 5 to said manual. It is not, however, included in the on-line version. 201 Report IN-023/2008 1.6.3. Propeller and engine overspeed criteria As indicated in 1.5, the aircraft pilot reported that the engine rpm’s climbed above 2,800, meaning that the maximum rpm rate of 2,700 specified for the engine and propeller type outfitted on the airplane was exceeded. As regards the propeller, its manufacturer, McCauley, specifies the inspection criteria for those propellers that have been exposed to overspeed conditions in Service Letter 1998- 23, dated 21-09-1998, included here as Appendix D. Specifically, for propellers installed in reciprocating engines that have not exceeded a 15% of the the maximum rated (takeoff) rpm’s, only a general external visual inspection is required. No additional actions are specified. The mechanism that changes the pitch on the propeller blades has physical stops that limit the turn rate on this propeller type to approximately 2,800 rpm. This rate is noticeably below the 2,980 rpm’s that would correspond to a 15% overspeed in this case. As regards the engine, its manufacturer, Lycoming, specifies the criteria for inspecting engines that have been exposed to overspeed conditions in its Mandatory Service Bulletin No. 369J, dated 22-11-2004, and which is also included here in appendix D. It defines the term “momentary overspeed” as “an increase of no more than 10% of rated engine RPM for a period not exceeding 3 seconds”, and states that an instantaneous overspeed is allowable in fixed-wing aircraft. It also establishes inspection criteria depending on whether the overspeed was less than or equal to 5%, between 5 and 10% or in excess of 10% of rated engine rpm’s. Specifically, for engines of the type outfitted on the incident airplane that do not exceed 5% of their rated rpm’s, it specifies that the causes of the overspeed must be determined and corrected. In this case the overspeed was 2,835 rpm’s. 2. ANALYSIS AND CONCLUSIONS The aircraft pilot described a situation in which the engine rpm’s climbed above 2,800, meaning that the maximum rated rpm’s for the engine and propeller type outfitted on the airplane were exceeded. The propeller pitch did not respond to his attempts to adjust it and the rpm’s only dropped when he set the throttle to idle. Then, when he opened the throttle slightly, the engine once again exceeded 2,800 rpm’s, the airplane vibrated and smoke smelling of oil entered the cockpit. The inspection of the power plant components revealed the presence of an oil leak at the governor-engine coupling. Additionally, as described in 1.4.3, the engine inspection showed damage that was consistent with a high rotation rate that may 202 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 even have involved an engine overspeed condition. Concurrent with this was the oil leak that hampered the lubrication of the engine and led to the overheating of the engine’s moving parts. Finally, the inspection of the propeller governor showed that even though the oil leak had affected its operation, the governor itself had not malfunctioned. Based on the inspection criteria specified by the respective engine and propeller manufacturers for components exposed to overspeed conditions, the situation described by the pilot would have corresponded to a momentary overspeed or, at most, to an overspeed below 5% of the engine’s rated rpm’s. These engine and propeller overspeed conditions alone should not have produced the damage found in the engine. In light of these considerations, it may be concluded that the damage found in the aircraft’s engine resulted from an engine oil leak in the area where the propeller governor is coupled to the engine. This leak gave rise to a gradual reduction in the amount of oil in the engine, with the ensuing drop in the flow of lubricating oil. The flow received by the governor was sufficient for its continued operation since its oil is supplied directly by the engine’s oil pump. Under these conditions, the engine’s moving parts overheated, leading to increased load torque in these components which would have tended to reduce their rotation rate. The governor reacted to this drop in rotation rate by reducing the pitch of the blades. Since the engine rpm’s did not recover, it is probable that the engine behaved in such a way that the propeller blade pitch was reduced to the minimum practically instantaneously, to the point where the blades could have reached their physical stops. This would have resulted in the sudden increase in rpm’s, which aggravated the damage already being caused by the engine’s moving parts. In the case at hand, Lycoming Service Instruction (SI) no. 1438A, dated 09-12-2005, is applicable in that is specifies that certain propeller governors must be coupled to the engine using two gaskets and a plate so as to eliminate the possibility of oil leaking between the governor and the engine accessory housing. Since the installation in this case was completed using a single gasket, the result was a leak that, at least initially, must have been small and slow to develop, as determined by the amount of oil recovered during the inspection, the time elapsed between engine start-up and when the pilot detected the overspeed, the extent of the warping of the engine’s internal components, and the fact that the engine oil pump and the propeller governor had sufficient oil to keep running at all times. Since the propeller governor is considered to be an aircraft component, the Aircraft Maintenance Manual must include the instructions for its proper installation and, as noted in 1.6.2, in this case, even though the manual included the modification issued as Temporary Revision no. 5, this revision had not been made available to users who accessed the electronic version of said manual. This is considered to have been a contributing factor to the incident. 203 Report IN-023/2008 3. SAFETY RECOMMENDATIONS Since, as noted in the last paragraph in 1.6.2, the manufacturer has yet to include Temporary Revision no. 5 to the electronic on-line version of its Maintenance Manual, reference D991-3-13, the issuance of the following safety recommendation is deemed necessary: REC 15/2011. It is recommended that the Cessna Aircraft Co. include Temporary Revision no. 5, dated 11-07-2005, to the on-line distribution of the electronic edition of its Maintenance Manual, reference D991-3-13, titled “Cardinal RG Series 1971 thru 1975 Service Manual”, dated 01- 09-1972, Revision 3, dated 01-09-1974, in addition to the temporary revisions already included in said distribution. The Manufacturer has accepted this Safety Recommendation. 204 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 205 APPENDIX A Cardinal RG Series 1971 thru 1975 Service Manual: – 13-7 a 13. Propeller Governorr – Temporary Revision Number 5 Report IN-023/2008 206 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 207 Report IN-023/2008 208 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 209 Report IN-023/2008 210 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 211 APPENDIX B Lycoming Service Instruction (SI) No. 14381, Report IN-023/2008 212 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 213 Addenda Bulletin 4/2011 Report IN-023/2008 215 APPENDIX C Special Airworthiness Information Bulletin (SAIB) NE-06-08 United States Federal Aviation Administration (FAA) Report IN-023/2008 216 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 217 Addenda Bulletin 4/2011 Report IN-023/2008 219 APPENDIX D Propeller and engine overspeed criteria: – McCauley Service Letter 1998-23AAAAAAAAC. – Lycoming Mandatory Service Bulletin No. 369J Report IN-023/2008 220 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 221 Report IN-023/2008 222 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 223 Report IN-023/2008 224 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 225 Report IN-023/2008 226 Addenda Bulletin 4/2011 Addenda Bulletin 4/2011 Report IN-023/2008 227