The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts.
Pilots of piston-powered twins know of the need to feather the prop on a dead engine, but occasionally the task does not get accomplished – sometimes through human error, sometimes through mechanical blockages.
In a recent accident, the pilot encountered a blocked propeller that could not be feathered.
The FAA began investigating the potential for additional accidents of a similar nature involving a propeller that could not be feathered either with or without engine rotation. In most pilot operating handbooks and Aircraft Flight Manuals, there are warnings of the consequences of single-engine operation with a windmilling (blocked) or non-feathered propeller.
However, the manufacturer of the recent accident airplane agreed to emphasize the critical operational configuration of the windmilling/blocked propeller on an inoperative engine by duplicating, or moving, this warning to other places in the POH/AFM.
If a light or medium twin is trying to fly on one engine when the other prop is not feathered, it is very possible the airplane will not be able to maintain altitude. In addition, should the other engine fail, as in during a fuel delivery problem, the non-feathered propeller will dramatically decrease the engine-out glide distance.
Propellers can be impossible to feather if the crankshaft fails or the pilot fails to feather before the prop windmills down to a speed that results in the start locks engaging.
Blocked propellers will also result if pilot attempts a restart, engaging the start locks, but the engines fail to start. Failure to properly complete the preflight feathering checks that should be published in the POH/AFM could also result in pilots encountering situations that result in a windmilling or blocked propeller.
The FAA is encouraging manufacturers to amend the POH and AFM manuals to increase pilot awareness to the importance of verifying the capability of the propeller to feather during preflight checks, as well as provide additional information on in-flight operations involving a windmilling/blocked propellers. Maintenance personnel are also cautioned to be alert during routine inspections of propeller installations to ensure that the start locks (centrifugal, pressure and inertia latching provisions) are being maintained properly.
Beech V35A Bonanza
Severe Structural Corrosion
The aircraft owner asked a repair facility to refurbish and clean the lower fuselage area under the floorboards.When the technician removed the floorboards, it appeared the floorboards had not been taken up since the aircraft was new. He removed the large floorboard section, just aft of the wing spar, and found severe structural corrosion on the two center channel assemblies used for mounting the seat rails.The report implies that past inspections were not properly accomplished.
Beech A36 Bonanza
Defective Engine Starter Drive
The starter would not crank the engine.The technician discovered the starter drive was severely galled, heat damaged and seized. It was the fifth starter drive failure in the aircrafts past 300 hours of operation. The technician discovered the oil galley for the starter drive was plugged along its entire length with a silicone sealer that apparently had been injected into the oil galley during an engine overhaul eight years and 300 hours earlier. He also found other damage inside the engine, including destruction of the crankcase and oil pump bearing surfaces along with large amounts of steel in the oil sump.Engine time since overhaul – 300 hours.
Beech E90 King Air
Pressurization System Defect
The crew reported the cabin pressurization system differential pressure was low.The technician found the outflow valve cone would hang up intermittently. He found the guide pin used to align the cone in the valve assembly was broken.Part total time – 5,000+ hours.
Cessna 172RG Cutlass
During an engine change, the technician removed the engine mounts for inspection and discovered the upper left engine mount bracket was cracked at the mount fastener hole. The inboard two rivets used to attach the bracket to the longeron hat section were missing. Part total time – 6,324 hours.
Cessna 172R Skyhawk
Defective Flight Instrument
A pilot reported the directional gyro tumbled in flight and would not re-erect.The technician could not find a defect with the instrument air supply and so he replaced the directional gyro, which solved the problem.Part total time – 295 hours.
Cessna 172S Skyhawk
Defective Propeller Spinner
The technician discovered the propeller spinner bulkhead was cracked.The corner of the spinner bulkhead assembly was completely ripped away and the edge of the spinner was beginning to peel up, possibly because of a manufacturing defect. The FAA Service Difficulty Program data base contains three other reports on similar propeller spinner defects. The part total times for these reports are 143, 50, and 41 hours operating time. Part total time – 42 hours.
Cessna 182Q Skylane
Seat Restraint System Failure
The pilot reported the copilots shoulder harness inertia reel locked up and would not release.The coil spring that is inside the inertia reel housing had broken and jammed the roller. The inertia reel assembly was manufactured in April 2001. It was installed on this aircraft on June 1 and failed on June 7. Part total time – 3 hours.
Cessna 320F Skyknight
Landing Gear Failure
The pilot could not extend the nose landing gear prior to landing.The left nose gear door was jammed into the wheel well, the door linkage was separated, and the bellcrank was broken. The incident occurred because the left nose gear door actuating rod attachment clevis pin fell out. The technician recovered the door retention pin and discovered that it was a cowling safety pin instead of the proper clevis pin.Part total time – 3,644 hours.
The aircraft owner reported a fuel odor inside the aircraft.The technician discovered the fuel crossfeed line beneath the floor was seeping fuel through several pinholes. This fuel line is routed from the left main fuel tank under the floor to the right fuel selector valve. The technician found corrosion inside the line that may have resulted from the fuel sump drains not being used for long periods of time. If the fuel line had broken, there would be no way to shut off the fuel supply coming from the tank.Part total time – 3,792 hours.
Grumman American AA-5 Traveler
The pilot noticed the right wing seemed heavy during flight. After landing, he found the right aileron was detached from the wing at the outboard end.The right outboard aileron hinge point was broken. The aircraft is normally parked outside on a ramp and the damage may have been caused by high winds.Part total time – 1,773 hours.
Piper PA-18-150 Super Cub
Defective Exhaust System
During a scheduled inspection, the technician discovered the engine exhaust system Y pipe was cracked adjacent to the weld and was in danger of separation. The technician discovered the inner baffle was also cracked.Part total time – 538 hours.
Piper PA-28-161 Warrior
Engine Starter Malfunction
The pilot reported that the starter continued cranking the engine after the key was removed. He also reported the starter turned the engine whenever battery power was present.A technician discovered the wrong starter solenoid was installed when the aircraft was manufactured. After removing and disassembling the starter solenoid, he discovered the electrical contacts were welded together.Part total time – 2,109 hours.
Piper PA-30 Twin Comanche
Defective Induction Air Box
The pilot lost directional control of the aircraft during takeoff and the aircraft departed the runway. The pilot reported the right engine would not develop full power during the takeoff run.The technician discovered the alternate air box door was loose in the air induction system and restricted airflow to the intake. He inspected the left engine air induction system and found the alternate air door in the bottom of the cowling.
Piper PA-31-350 Chieftain
Defective Fuel Pump
While performing a scheduled inspection, the operator observed the right engine fuel pressure was 34 PSI at 1500 RPM. The technician adjusted the engine-driven fuel pump up one-half turn but the fuel pressure was unchanged. After several adjustments without improvement, he removed and replaced the fuel pump. The fuel pressure remained at 34 PSI from idle to approximately 1,900 RPM.The submitter reported finding eight new style (/M) fuel pumps that produced low fuel pressure with no low to midrange adjustment.
Piper PA-32-300 Cherokee Six
Wing Spar Structural Damage
While replacing a wing skin, a technician discovered severe corrosion damage on a wing spar.The left wing lower aft surface of the forward spar was damaged just outboard of the main gear attachment casting. The corrosion was centered around a rivet, and the metal was badly exfoliated. There were several other corrosion sites in the same area that had not progressed to the severe stage. Also, a fastener hole for the attachment of the main gear casting displayed signs of serious corrosion.Part total time – 3,195 hours.
Piper PA-32R-300 Cherokee Lance
Electrical System Anomaly
The pilot reported the amp meter fluctuated just before he lost electrical power to the avionics.The avionics wire terminals on the master switch were loose. The terminal retaining screws were not properly tightened during the previous installation. There was evidence of arcing between the wire terminals and the master switch.
Piper PA-34-200T Seneca
Landing Gear Failure
During a landing approach, the pilot attempted to lower the landing gear without success. When he used the emergency extension system, the landing gear went to the down-and-locked position.The hydraulic system reservoir was empty. A seal inside the nose landing gear actuator was deteriorated and allowed the hydraulic fluid to leak.Part total time-7,072 hours.
Piper PA-46-310P Malibu
Defective Engine Mount
While changing the engine, a technician noticed a damaged engine mount.The engine control cables were chafing hard against the lower left engine mount tube assembly. The engine mount assembly also gives structural support to the nose landing gear installation. He determined the damage was caused by improper support of the engine and propeller control cables. The Adel clamps, which provide support as well as clearance, were not installed. Part total time – 3,890 hours.