January 1, 2005
By Bruce Landsberg
Bruce Landsberg, executive director of Air Safety Foundation, still believes that good maintenance is a sound investment.
We've all seen aircraft that are better left parked. They're called hangar queens, junkers, derelicts, or wrecks. Many of them don't fly much but some fly a great deal, much to everyone's consternation. These machines have so many discrepancies that the odds for safe flight are often in question, but sometimes fate has a surprise.
A Piper Malibu Mirage landed on an unlit ranch landing strip to drop off a passenger on a midwinter evening. The 3,400-foot-long runway (which also served as a ranch road) was surrounded by rolling hills. A parked car with the headlights shining down the runway provided approach guidance. This is not a recommended practice, by the way, for arriving on a 30-foot-wide runway, but with the high-risk landing out of the way the pilot took off about half an hour later.
The weather was clear with calm winds. Local residents reported hearing what sounded like an airplane taking off, followed by a loss of engine sound and an impact or explosion. The flight instruments in the wreckage showed a slight left bank and nose-low attitude, with the two vertical speed indicators showing 2,000 and 4,000 feet per minute down. It was a fatal impact.
The pilot reported more than 12,000 hours on his last medical application, but his logbooks weren't recovered so not much else is known about time in type, recency of experience, or night currency.
This Mirage could charitably be described as "neglected." The airframe was estimated to have about 4,200 hours and was on its fifth engine. At just more than 800 hours per engine, on average, it appears that mechanical longevity eluded this aircraft. The last annual inspection occurred 12 months and about 300 flight hours before the accident. Five months before the accident, an FAA-certified repair station had given the pilot-owner a 15-item list of "grounding discrepancies," which included: a cracked nose cowling; fraying seat belts; left mag switch broken; left window cracked; left windshield crazed; stall warning inoperative; turbine inlet temperature (TIT) gauge inoperative; door latch safety inoperative; several hydraulic components leaking; main gear trunnion pins worn; several cracks in wing lower skins; fuel leaks; loose rivets on right flap; wing spar bolts loose; and elevator trim cable frayed. Any one of these items could have led to a serious mishap. According to the shop manager, the only item that had been repaired prior to the accident was the cracked nose cowling.
When examining the wreckage, investigators found open circuit breakers for the engine monitor, hydraulic pump control, turn coordinator, flap motor, nonessential bus, GPS (global positioning system), and the number-one automatic direction finder (ADF). After-market instrument panel inoperative stickers were found on the panel. Directly in front of the pilot was one stating, "Pressurized flight prohibited," and below the annunciator light panel was one stating, "Low vacuum warning inop." Several lamps were missing from their respective receptacles. It might have been easier to list the equipment that was working.
A coworker noted the pilot had been operating the airplane for about four months with the landing gear in the down position because of "some mechanical problem." The shop manager explained that the gear hydraulic power pack was damaged from running the pump out of hydraulic fluid. The pilot could not afford a new pump, nor could he afford to resolve the other discrepancies. In an e-mail to the shop more than seven months before the accident, the pilot described the problem as, "The nose gear is not fully extending and locking." The e-mail also read, "Should any of my surviving family or attorneys try to hold you responsible for any potential future mishaps that are related to this landing-gear issue, please feel free to show them this correspondence as proof that I absolve you, your staff, and insurance carrier of any responsibility."
On big turbocharged engines such as the Mirage's, precise engine monitoring is essential. Lycoming and Piper required the TIT system to be functioning at all times for proper engine temperature control. Lycoming provided additional operating recommendations to the pilot's operating handbook (POH) that stress the importance of temperature control and the destructive effect of overtemping. There were mandatory service bulletins limiting TIT probes to 250 hours and requiring inspection of the turbochargers and tailpipes for in-service wear and damage.
After the accident, the engine was disassembled down to the crankshaft, and mechanical gear train continuity was confirmed. Finger compression was established on all cylinders. Magneto timing was checked. One magneto functioned and one did not. The oil filter was cut open and found to be free of foreign material. The right turbocharger shaft nut was missing and the blades were damaged. The left turbocharger was heat stressed and distorted with major damage from overtemping. This was deemed to have occurred before the accident. One of two dry air vacuum pumps was inoperative from an existing sheared drive coupling — that is, the pump was inoperative before the accident.
The damaged TIT gauge and probe were sent to an FAA-approved repair station for functional testing. The indicator met the manufacturer's specifications for a bench test but the probe failed a subsequent bench test. The damaged stall-warning-system lift computer and lift transducer were also tested. The lift computer met all test specifications but the lift transducer was inoperative, as previously reported in the shop's grounding discrepancies.
The landing-gear hydraulic power pack was tested and failed, as expected. Five service bulletins were not complied with. Disassembly revealed contamination inside the reservoir system with subsequent fouling of the pressure switches.
About a week before the accident a safety counselor asked the FAA to conduct a ramp inspection of the airplane and the pilot. The counselor felt that the pilot needed a "wake-up call." His concerns were a broken main cabin door restraint, flights with the landing gear extended, and the "very poor visual appearance" of the airplane.
Unless an airplane is in revenue service, such as air taxi or rental use, owners do not have to comply with service bulletins, even "mandatory" ones. However, good operating practice and common sense would suggest that there is a legitimate reason for most of these bulletins. Through warranty claims and outright failures, the history of the fleet will show where repairs need to be made.
So which of the many serious faults that were detailed on the shop's list brought the Mirage down? An engine malfunction resulting from detonation, fuel flow interruption, instrument malfunction, failed elevator control because of the frayed cable, or cabin door unlatching were all possibilities. During post-accident examination of the wreckage, investigators verified that many of the listed discrepancies still existed; however, none of these were responsible. The pilot's failure to maintain control on a dark night during the initial climb resulted in the crash. It's an unfortunate ending to a long story of aircraft neglect, and it proves that the most obvious probable cause sometimes isn't.
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