High-altitude operations are known to require extra care and attention. The thinner air reduces takeoff and climb performance when compared to sea level. While a turbocharger helps overcome reduced engine power, even it must be managed correctly to obtain maximum performance. Problems can arise if the crew doesn’t have much experience with high-altitude takeoffs and might not be exercising every precaution.
In such circumstances, pilots unfamiliar or inexperienced with turbocharged engine operation might be tempted to apply techniques for non-turbocharged engines at high altitude. That generally means leaning for best power at takeoff, although a turbocharged engine may not require leaning at most altitudes or, if it does, not nearly as much as a normally aspirated powerplant. It’s easy to get wrong, and that may be what happened to a Turbo Saratoga a couple of years ago.
Background
On August 25, 2012, at about 2145 Pacific time, a Piper PA-32-301T Turbo Saratoga impacted trees shortly after departing California’s Lake Tahoe Airport. The five occupants, which included left- and right-seated private pilots, were fatally injured; the airplane was destroyed. Nighttime visual conditions prevailed.
When the airplane arrived earlier that day and while taxiing to the ramp, its engine shut down and it took numerous attempts for the pilots to restart it. Upon parking, the pilots reported difficulties establishing the proper fuel/air ratio at such a high density altitude to prevent temperatures from exceeding normal parameters. They also indicated this was their first time at the airport.
Numerous witnesses heard the airplane depart and noticed the engine noise sounded labored, as if it was not producing full power. Some heard three “chirps,” that sounded if the tires were touching back on the runway surface after becoming airborne. Footage from a security camera appeared to depict the airplane take off and begin a climb. The airplane appeared to level off and then a flash of light occurred in the area of the accident site.
Investigation
The accident site was about 0.43 nm from the departure end of Runway 36 on a 359-degree heading. The main wreckage came to rest inverted in tall brush and was consumed by a post-impact fire.
The wing-flap handle was between the fully retracted position and first notch (10-degree) setting. The stabilator’s pitch trim system was consistent with a position of about a three-degree nose-up attitude.
The engine displayed no evidence of pre-impact catastrophic mechanical malfunction or fire. The single-drive dual magneto was found securely clamped to its mounting pad but sustained damage, rendering it inoperative. It could not be functionally tested.
The crankshaft was rotated by hand in both directions, using the propeller. Compression was observed in each cylinder. Mechanical continuity was established throughout the rotating group, valve train and accessory section during hand rotation of the crankshaft. The engine’s cylinders were consistent with normal operation.
The turbocharger compressor and turbine impellers remained intact and undamaged. The turbocharger was disassembled and remained free of pre-impact anomalies. Each exhaust system clamp was secure at each location. The exhaust bypass butterfly valve remained intact and undamaged.
Additionally, the fuel pump installed on the engine was determined to be incorrect. There was no record indicating when the original fuel pump was removed and the one found at the accident scene was installed.
Weight and balance computations were made for the accident takeoff, based on the airplane’s empty weight, total moment and center of gravity obtained from its maintenance records. For the takeoff, the airplane’s gross weight was about 3557 pounds and the center of gravity was 91.78 inches. The airplane’s maximum gross takeoff weight was 3600 pounds, with the center of gravity range at that weight between 90 and 95 inches forward and aft, respectively. Accordingly, the airplane was within its weight and balance limitations when the takeoff began. According to manufacturer’s data, the airplane would have required just under 3000 feet to take off and clear a 50-foot obstacle. The departure runway was about 8540 feet long.
Weather observed about 10 minutes after the accident included wind was from 200 degrees at three knots, temperature of 16 degrees C, a clear sky and an altimeter setting of 30.08 in. Hg. Density altitude was 7751 feet.
There was no evidence of pre-impact mechanical malfunctions or failures found during the examination of the airplane that would have precluded normal operation. Although it could not be confirmed, it is likely that the left-seat pilot was the flying pilot and that the right-seat pilot, who owned the airplane and had been consuming alcohol before the flight, was not the pilot-in-command.
It’s not clear how much experience the pilot/owner in the right seat had with the airplane at high-altitude airports like Lake Tahoe’s. An acquaintance of the pilot/owner advised him to lean the airplane’s engine while operating on the ground at high-elevation airports. He speculated that the pilot may have followed his advice, but then failed to enrich the mixture prior to departure.
Probable Cause
The NTSB determined the probable cause(s) of this accident to include: “A partial loss of engine power for reasons that could not be determined because examinations revealed no evidence of mechanical anomalies with the airframe or engine that would have precluded normal operation and the pilots’ decision to continue the departure in dark night conditions with the engine not producing full power.”
It’s easy to think the pilots mishandled the mixture control on the takeoff. Given the apparent difficulty the two had managing the mixture control when the airplane arrived earlier that day, it’s certainly conceivable the mixture control wasn’t at an optimum setting for the takeoff. The pilot/owner’s consumption of alcohol during dinner—coupled with the reduced oxygen available at the airport elevation—probably didn’t help.
Leaning a turbocharged engine for a takeoff like this might not have been necessary. The incorrect fuel pump likely didn’t help things, but the most likely scenario is mismanaging the mixture control.
