PIPER PA-30 — Winston-Salem, NC

What happened

Near the conclusion of the cross-country flight, when the airplane was flying about 2,175 ft pressure altitude and about 4 nautical miles due west of the approach end of runway 4 at the destination airport, the pilot broadcast on the frequency that one engine was not making as much power as the other, but that, “we’re ok.” The controller cleared the pilot to land on runway 4; however, for reasons that were not reported by the pilot, the airplane continued past the extended runway centerline for that runway. The pilot subsequently asked to land on runway 33, which was approved. The airplane continued on an easterly heading past the extended runway 33 centerline, then turned left on northwesterly heading flying parallel to runway 33. While flying east of the airport one witness noted the airplane banking left to about 45° before the wings rolled level and then banked about 10° to the left. The same witness reported that, while flying in a nose-up attitude just above the trees with the landing gear extended, the airplane rolled to an inverted position and descended straight down. The airplane impacted terrain behind a house.

Postaccident examination of the flight controls, propellers, right propeller governor, left engine and its systems, and right engine powertrain, lubrication, exhaust, ignition, and air induction systems revealed no evidence of preimpact failure or malfunction. Neither propeller was feathered at impact. The damage to the left propeller was consistent with the engine developing some power at impact while the lack of damage to the right propeller was consistent with windmilling/rotating and not developing power at impact. Additionally, although it was not determined if there were any missing vortex generators (VG’s) on either wing at the time of the accident, the airplane’s performance was not changed by the installation of the VG’s. Thus, if any were missing at the time of the accident, it likely did not contribute to the accident.

Postaccident operational testing of the right engine’s fuel servo revealed that it passed all four test points and the regulator hysteresis check, but it failed testing of the idle circuit, which should result in decreased fuel flow with movement of the throttle control from wide open to idle. The fuel flow when reducing the throttle to idle was about 2.6 times higher than what it should have been. Disassembly of the right fuel servo revealed internal contamination in the fuel section of the regulator that was determined to be acrylonitrile-butadiene-styrene (ABS), a thermoplastic, though the exact source of the contamination could not be determined. Following reassembly of the regulator with the internal contamination removed, the idle circuit test was repeated multiple times, and the fuel flow was within limits. Although it could not be determined if the excessive fuel flow during the idle circuit test was caused by the internal contamination or a combination of that and misalignment of the regulator section, the additional 0.011-inch clearance of the throttle valve at idle was likely the result of maintenance personnel attempting to remedy the excessive fuel flow when moving the throttle valve to idle. Thus, it is likely that during the descent approaching the airport with both engines operating at a reduced power setting, the excessive fuel flow to the right engine likely resulted in a total loss of engine power.

Although the right engine likely sustained a total loss of engine power due to a malfunction of the fuel servo, it is likely that the pilot either did not, or delayed, feathering the right propeller until the propeller rpm slowed to where the propeller blades engaged on the start locks. In that position, an attempt to feather the propeller would not be possible until the propeller rpm increased above the speed that disengaged the start locks. The increased parasitic drag from the windmilling and unfeathered right propeller likely precluded the possibility of straight and level flight. Towards the end of flight, the airspeed likely reduced below the published Velocity Minimum Control (Vmc) speed, and the airplane rolled to an inverted position. Had the pilot either turned towards runway 4 which was the nearest runway after advising the controller of an engine malfunction, or feathered the right propeller following total loss of right engine power and maintained an airspeed above the published Vmc speed while continuing towards the airport, it is likely that he could have reached the airport and landed uneventfully.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.