Turbo Troubles

Turbocharged engines not tolerant of exhaust system faults


The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts.


A recent fatal accident of a single-engine aircraft involved the apparent separation of the tailpipe assembly from the turbocharger, which allowed hot exhaust gases to be expelled into the engine compartment.

The pilot reported smoke and fire in the cockpit before the aircraft crashed short of the airport, killing both aboard. The NTSB investigation is targeting an exhaust clamp failure due to fatigue cracks found in the turbocharger to tailpipe clamp. A review of the FAA Service Difficulty Report (SDR) database reveals similar incidents involving this clamp as a primary factor.

This accident highlights the need to vigilantly follow exhaust system maintenance procedures. Annual and 100-hour inspection programs require an inspection of all exhaust system components. Maintenance personnel should follow the instructions provided by each manufacturer for specific inspections or maintenance on exhaust system components, including turbocharger installations. It is important to note that many manufacturers do not recommend welding of cracked exhaust system components.

This particular aircraft had maintenance record entries for two turbocharger replacements since the aircraft was new. These episodes would have provided an excellent opportunity for conducting a thorough inspection of the clamp and flange area in question.

The aircrafts maintenance manual revealed a specific procedure for inspection of the multi-segmented V band clamp that secures the tailpipe to the turbocharger. These multi-segmented clamps typically utilize spot welds to secure the segments to the outer band. It also provides a procedure for properly torquing the clamp upon reinstallation and instructions for periodic inspection of the complete exhaust system. A recommended replacement time for the clamp is also provided.

Exhaust system defects will continue to be a problem due to heat, vibration and dissimilar metals. Maintenance personnel should review exhaust system maintenance practices provided by the manufacturer and follow those instructions when servicing aircraft.

Beech A-36 Bonanza
Defective Structure

During a scheduled inspection, a technician discovered a crack in the avionics shelf assembly.The avionics shelf attachment bracket was cracked in a bend radius at the aft end. The technician found another crack in the bend radius at the upper corners.The problem may have been caused by in-flight vibration.Part total time – 4,716 hours.

Beech 65-80 Queen Air
Wing Flap Failure

During a landing approach, the wing flaps failed to extend. A technician found the flap drive motor operated but did not drive the flaps because all the teeth were stripped on the gear used on the flap motor armature shaft.Part total time – 377 hours.

Beech 100 King Air
Defective Flight Control Component

After finding a defective stabilizer actuator, the technician ordered a replacement part.When the overhauled actuator was received, the technician conducted a receiving inspection and found dirt and corrosion in the upper attachment bearings, and the lower attachment bearings were stiff. The general appearance of the unit was questionable.The technician installed the actuator and conducted an operational test but noted several shortcomings in the unit.Part total time – unknown

Beech 100 King Air
Defective Wing Attachment

During a scheduled inspection, a technician discovered the left wing attachment bolt, used at the left wing aft upper attachment point, was cracked. The crack was located at the junction of the bolt head and the shank.A similar inspection was conducted one year prior to this finding and no defects were noted at that time.Part total time – 3,616 hours.

Cessna 172 Skyhawk
Flight Control Discrepancy

During an annual inspection, a technician discovered the right outboard aileron hinge pin had migrated out approximately 5 inches. One aileron hinge lobe cotter pin was still installed, and the other pin was only partially in place. AD 83-22-06 deals with this subject but they do not apply to the serial number or year of manufacture (1956) of this aircraft.

Cessna 172R Skyhawk
Seat Structural Defect

While conducting an annual inspection, a technician discovered the copilots seat pan had a 1.5-inch crack in both aft corners, compromising the structural integrity of the seat.Part total time – 780 hours.

Cessna 172R Skyhawk
Erroneous Fuel Quantity Indications

A flight school maintenance department received numerous reports of the low fuel warning light flickering during flight. The warning light flickered so fast pilots could not determine if it was for the left or right tank.Maintenance personnel had been unable to duplicate the fault on the ground. After a similar recent report, a technician removed the left fuel-quantity sending unit and observed that the left low fuel light illuminated as the float arm passed through the 24-gallon level. The left fuel quantity indicator needle dropped to zero during this test.Many of the operators pilots have reported erroneous fuel warning lights in 9 of the 10 like aircraft. The problem is almost always intermittent, which makes it difficult, if not impossible, for the maintenance personnel to duplicate.Part total time – 1,742 hours.

Cessna 210N Centurion
Landing Gear Failure

During a landing approach, the pilot placed the landing gear control in the down position. The right main gear did not respond and all efforts to extend the gear failed. The pilot had to make a gear-up landing.While assisting the removal of the aircraft from the runway, a technician noticed the right main gear actuator would not extend or retract. Upon further inspection, he discovered the actuator was cracked.This defect was addressed in Cessna SEB 01-2.Part total time – 14,625 hours.

Grob G120A
Defective Fuel System Indication

After starting the engine for a flight, the pilot noticed the fuel-flow indication was zero. A test of the fuel-flow system revealed that tapping on the indicator face made the gauge work. After he replaced the fuel flow transducer, the system operated properly.Part total time – 9 hours.

Luscombe 8A Silvaire
Structural Damage

During an annual inspection and compliance with AD 55-24-1, a technician discovered severe structural damage of the aft carry-through spar.The bottom web suffered the long-term effects of intergranular corrosion that had seriously compromised the structural integrity of the center wing carry-through structure. If this had not been corrected, it could have resulted in a catastrophic failure.Part total time – 1,821 hours.

Piper PA-18-150 Super Cub
Fuel Leak

This float-equipped aircraft was modified by installation of STC SA02171AK, which involves installed 24-gallon fuel tanks in each wing.While investigating the cause of a reported fuel leak, a technician discovered the fuel tank was leaking along the lower welded seam on the outboard side, apparently because of an insufficient amount of material along the welded seam.Part total time – 220 hours.

Piper PA-28-151 Warrior
Poor Engine Operation

During a ground test, the engine performance was very poor, due to an apparently excessively rich mixture. The technician removed the Marvel carburetor throttle body assembly and discovered the needle valve would not seat. He found a piece of metal lodged between the needle and the seat.The sliver appeared to be aluminum and was approximately .188 inch long, .018 inch thick, and .023 inch wide. It may have been a portion of the female threads used to attach the fuel inlet and strainer assembly to the throttle body. Part total time – 4,000 hours.

Piper PA-28-161 Warrior
Landing Gear Failure

During a landing, the left main landing gear assembly separated from the aircraft.The left main gear attachment sheared at the upper and lower retaining bolts. This aircraft was used for flight training for a long period of time and may have been subjected to many hard landings.Part total time – 12,250 hours.

Piper PA-32RT-300T Turbo Lance
Nose Landing Gear Failure

During a landing approach, the pilot placed the landing gear control in the down position and noticed the nose gear did not fully extend. While on a short final, the nose gear went to full down and locked.During a ground test, the gear failed to retract and the hydraulic powerpack would not run. A technician noticed the hydraulic motor was hot and the hydraulic reservoir was empty. While replacing the hydraulic powerpack, the technician noticed evidence of a leak at the female threads of a cross fitting located just below the powerpack. Further inspection revealed that three of the four bosses had hairline cracks and one was leaking.Part total time – 3,046 hours.

Piper PA-44-180 Seminole
Defective Induction Air System

During a scheduled inspection, a technician discovered the left engine carburetor heat airbox was cracked at the hot air inlet, and the crack extended almost all the way around the tube circumference. The FAA Service Difficulty Program database contains five additional reports of failed welds at this location.Part total time – 299 hours.

Piper PA-44-180 Seminole
Carburetor Heat Failure

During an engine runup, the pilot found there was no RPM drop on the right engine when carburetor heat was applied. A technician discovered the carburetor heat control cable had broken where the threaded shaft is swaged onto the cable. The shroud that goes around the shaft was missing.During a previous 100-hour inspection, both engine throttle controls and the right engine mixture control displayed signs of extreme wear and damage and were replaced. While these controls had not yet failed, the shrouds had come loose and were floating freely on the threaded shaft. Part total time – 577 hours.

Piper PA-46-500TP Meridian
Propeller Governor Damage

During a scheduled inspection, a technician discovered the overspeed governor wiring was damaged.The overspeed governor is located on the forward left side of the engine. The electrical plug for the overspeed governor test solenoid is positioned in a manner that causes damage to the wires when the cowling is removed or installed. The electrical plug for the wiring is straight, and the submitter suggested that a 90-degree plug might alleviate future wire damage.


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