Safety Case Studies

Accident Case Studies examines aviation accidents that involve maintenance as either a probable cause or factor. The information in Accident Case Studies is obtained from National Transportation Safety Board (NTSB) reports, regulatory authorities and accident investigation bureaus, and research by the Aviation Maintenance staff. The information in Accident Case Studies is presented here to help the aviation maintenance industry learn from accidents and incidents and prevent future mistakes.

Homebuilt Vans RV-6, near Longmont, Colorado, April 22, 2005. Onboard, one pilot. No fatalities. The pilot was not injured during a forced landing following engine failure in the Vans RV-6 that he had just purchased. Prior to test flying his new airplane, the oil and filter were changed and cylinder compressions checked. Compressions were normal. The RV-6 had received its annual condition inspection six months and seven tachometer hours prior to the accident. After the test flight, the new owner noticed that the engine oil was down about half a quart. There were six quarts of oil on the dipstick when the pilot prepared the RV-6 for the flight to Kansas. He planned to make a fuel stop in Longmont. The engine vibrated and lost power as the pilot began descending to Longmont's Van Brand Airport, then quit completely. The pilot was able to land in a field three miles from the airport, and the airplane was substantially damaged, according to the National Transportation Safety Board. The NTSB investigator-in-charge examined the engine after the damaged airplane was moved to a facility at Greeley, Colorado, and found that three quarts of oil remained in the engine. There was a crack in the crankcase below cylinder number two and the four connecting rod journals and caps showed "discoloration and heat signatures consistent with oil starvation," according to the NTSB report on the accident. "No debris or contamination was noted within the crankshaft oil passages. The crankshaft main bearings were secure and the main journals were undamaged. No discoloration was noted in the cylinder bores and the piston rings were intact." The NTSB found that the Christen inverted oil system's separator had a black residue inside, which partially blocked the ports of the separator. A Lycoming service instruction (No. 1397) recommends that the inverted oil system be flushed every 300 hours "as a means of forestalling any problems that may arise from residue in the inverted oil system..." Evidence that the separator is clogged with residue is shown by oil that is exhausted overboard through the oil breather. "No logbook entries," the NTSB report stated, "were noted for compliance with Lycoming Service Instruction No. 1397; however, no entry was required by [FAA] regulations."

Piper PA28-161 Warrior, Groveland, Florida, April 15, 2005. Onboard, one pilot. No fatalities or injuries. The pilot-mechanic planned to fly the Piper Warrior from Seminole Lake Gliderport to Kissimmee Gateway Airport after repairing the engine, which had caused an aborted flight the previous day. The mechanic replaced damaged parts on the number two cylinder, including a bent pushrod, pushrod housing, seals and lock tab, then performed a full-power static runup on the engine. After takeoff, about two miles from the runway, the engine started running rough, according to the NTSB report. The pilot-mechanic returned to the gliderport "and after recognizing he was going to overshoot the runway with the engine not producing full power, elected to perform a 360-degree turn back onto final approach. During the turn, the aircraft impacted trees and came to rest in a swamp south of the south edge of Runway 18." An FAA inspector performed a post-accident inspection of the engine and noted that the rotator-type valve stem cap was missing from the exhaust valve on the number two cylinder. "Damage to both ends of the No. 2 cylinder exhaust valve pushrod was noted," the NTSB report stated, "no evidence of a stuck valve was noted." That cylinder's exhaust valve guide was found to be within new limits per Lycoming specifications.

Bombardier CL-600 Challenger, Tupelo, Mississippi, March 9, 2005. Onboard, two pilots, five passengers. No injuries or fatalities. During a normal takeoff, when the Challenger reached V1 speed, the pilot-in-command tried to rotate the nose by pulling aft on the control column, but the column would not move back, according to the NTSB report. "The aft movement beyond the neutral position felt as if it was locked against a stop," the report stated. At about the 4,000-foot mark along the runway and after reach 140 to 145 knots, the pilot-in-command called for an abort, actuated the spoilers, and applied maximum brakes and maximum reverse thrust. During the abort, the pilot said he either felt or heard a "crunch" as he continued to apply back pressure on the control column. He told the NTSB, "something may have given and the control column may have moved aft of the neutral position. No one was injured after the Challenger continued off the end of the runway and finally stopped after the nosewheel collapsed. During the subsequent investigation, the accident pilot pulled the control column aft to the nose-up stops and the column moved freely, with no jamming evident. However, investigators found that a fairing on the base of the copilot's control column showed evidence of missing paint "where the microphone jack receptacle overlaps the control column base fairing during control column rotation," according to the NTSB report. "No paint was missing on the pilot's side of the control column base fairing," which also has a microphone jack installed. The investigator again had the pilot pull the control column aft, but this time applied slight finger pressure to the copilot's microphone jack. "When the microphone jack box contacted the fairing at the control column base, the control column could not be moved further aft. The accident pilot stated the position of the pilot's control column in this jammed condition appeared to be similar with the control column position encountered during the accident sequence." After the accident, the FAA released an airworthiness directive (AD2005-11-04) covering Bombardier airplanes modified by STC4900SW (a modification that was done to the accident Challenger). Until the microphone jack assemblies are modified to prevent control column jamming, visual inspections must be done on both control columns "to detect damage that may interfere with movement of the control column," the NTSB report stated.