Safety Case Studies

Gaps in procedures and less than professional attitude leads to engine power loss.

MECHANIC BLAMED FOR AIRPLANE CRASH ON HIGHWAY

The plane landed on a minivan in which a 12-year old girl was a passenger, and its propeller nearly sliced off the girl's entire left leg, leaving it attached to her body with just a shred of tissue. She has undergone at least five surgeries since. The pilot and his son were unhurt.

The National Transportation Safety Board (NTSB) ruled that a mechanic used improper parts to repair the engine on the Piper Turbo Arrow plane, failed to check whether pieces of a damaged valve had fallen into the engine, and spent just three hours to complete a job that should have taken about 20 hours.

The rented airplane lost power at about 150 feet of altitude departing Buchanan Field Airport (CCR) in Concordia, Calif., and the pilot elected to land on the I-680 freeway. He struck two vehicles on landing, the second of which contained the girl. The force of impact spun the airplane around, and the propeller struck her (all three propeller blades were bent opposite the direction of rotation). A split in the wing tank resulted in spilled fuel, and the aircraft was demolished by fire.

The pilot later told investigators, "As I approached the end of the runway, I experienced a dramatic power loss ... I was not able to gain altitude from that point forward. ..."

"I slowed the aircraft and landed on a nearby highway. The aircraft impacted one or more vehicles during landing and then came to rest up against the traffic median," he explained. "Both wings were on fire. My son and I exited the aircraft via the right-side passenger door."

Investigators quickly focused on the Teledyne Continental Motors (TCM) engine, model TSIO-360-FB. The number 2 cylinder was replaced immediately before takeoff. It had been fitted incorrectly with a 7.5:1 compression ratio piston; the replacement was the correct 8.5:1 compression ratio. From the investigation report, we glean that all was still not copasetic with the engine:

"Cylinders 2, 4, and 6 were mechanically damaged by what the TCM representative reported to be a foreign object. The number 4 cylinder combustion chamber contained a foreign object that appeared to be a portion of a valve head. The number 2, 4, and 6 top and bottom spark plus were mechanically damaged. The pistons that were installed in cylinders 1, 2, 4, 5 and 6 were 8.5:1 compression ratio pistons, which are certified for use in the IO-360 series engine. The piston installed into cylinder number 3 was a 7.5:1 compression ratio piston, which was the incorrect piston for the accident engine. ... The turbocharger turbine wheel exhibited foreign object damage."

The mechanic who performed the engine work was interviewed. From the notes of that interview, NTSB investigators relate the following:

"Inspector Pollard asked ... where [cylinder 2] came from and was it traceable. [The mechanic] said his boss ... gave it to him off the shelf in the shop where they had two or three and stated it was serviceable. ... I asked how did he determine it was serviceable and he explained he assumed it was.

"Note: the cylinder installed did not have any certification paperwork attached to it and it could not be traced to where it came from at the time [the mechanic] installed it on the aircraft.

"When asked about the manual requirements to install the cylinders, [the mechanic] stated he could install a cylinder from memory because he had done it so many times. `I could even install it blind folded,' [he] stated. [He] stated he did not have a maintenance manual available during installation.

"Note: the engine maintenance manual, section 5-50-00, UNSCHEDULED MAINTENANCE, states, `No unscheduled maintenance of the categories listed above should be attempted without consulting the applicable related publications. This includes part replacement.'

"When questioned if [he had] used a torque wrench to tighten the nuts, [the mechanic] stated he did use a torque wrench, however it did not have a calibration sticker ... I questioned what was the proper sequence as described in the manual. He explained the top big bolt first then the bottom small bolt. He only accounted for (4) four bolts. He stated the torque for the large bolts was 42 foot-pounds or 504 inch-pounds and the small bolts 34 foot-pounds or 408 inch-pounds.

"Note: the maintenance manual calls out the torque in inch-pounds ... by bolt number ... The torque is performed wet with engine oil on the threads.

"When questioned if [he had] performed a compression test on the replaced cylinder, [the mechanic] stated, `No, he did not perform a test using a gauge.' [The mechanic] stated he could perform a compression test by feel and that is what he did. `I can pull the propeller though, I can tell if there is 70 pounds or less.' ...

"I asked if [he] gave the pilot a return-to-service entry. [He] stated he did not provide the pilot with a return-to-service entry. [The mechanic] stated the pilot took the aircraft knowing that the turbocharger might have been damaged. I asked if he really explained about the turbocharger being damaged to the pilot and [he] stated, `I assumed the pilot knew what would happen'"

Lawyers for the girl's family will no doubt have a field day with the maintenance history and the cavalier attitude revealed in the NTSB report.

OPTIONAL COMPLIANCE LEADS TO AN ACCIDENT

From the UK's Air Accidents Investigation Branch is this March 28 report, which indicates that the accident resulted from the failure to make service bulletin compliance mandatory. It concerns a Socata general aviation accident at Nottingham Airport:

"During a touch and go landing, as power was applied, a propeller blade detached. The resulting imbalance caused both the crankshaft to fracture (allowing the propeller to be released) and the engine to partly separate from the structure. Metallurgical examination indicated the presence of fatigue in the propeller hub. The location and nature of the fatigue was similar to that described in an existing Service Bulletin, however that document has not yet been classified as mandatory." (See www.aaib.gov.uk/publications/special_bulletins/s2_2006_socata_tb10_g_bnra.cfm)