The following information provides an awareness of problems that might be avoided in the future. The information is based on final reports by official investigative authorities on aircraft accidents and incidents.
Two Lost Consciousness
Boeing 737-300. Substantial damage. Two minor injuries.
The U.S. National Transportation Safety Board (NTSB) determined that the improper installation of a fuselage crown skin panel led to fatigue cracking at a lap joint and to the eventual separation of the panel as the 737 was climbing through 34,000 ft during a scheduled flight from Phoenix to Sacramento, California, the afternoon of April 1, 2011.
The tear in the fuselage skin resulted in a rupture of the pressure vessel that caused the cabin to depressurize rapidly and two of the 125 people aboard the airplane to sustain minor injuries after losing consciousness.
The flight crew conducted an emergency descent and landed the 737 without further incident in Yuma, Arizona.
The NTSB report said that the flight had proceeded normally until the cockpit area microphone recorded an unidentified sound. Shortly thereafter, the captain detected the depressurization, declared an emergency and initiated an emergency descent. “The flight crew descended the airplane to 11,000 ft within five minutes,” the report said.
All but two people aboard the airplane donned oxygen masks soon after the depressurization occurred. A flight attendant in the forward cabin lost consciousness while attempting either to call the captain on the interphone or to make a passenger-address system announcement. He fell and struck a partition, which cut and broke his nose.
The report said that the flight attendant’s “incorrect assessment of his time of useful consciousness” was a contributing factor to his injuries. “Although [company] training materials indicated that the first action a flight attendant should take after a decompression was to take oxygen from the nearest mask immediately, he stated that he thought he ‘could get a lot more done’ before getting his oxygen mask on.”
One of the passengers, an off-duty employee of the airline, lost consciousness while attempting to assist the injured flight attendant. The passenger fell and sustained a cut above his eye.
After the emergency descent to 11,000 ft, the flight crew received further clearance to descend to 9,000 ft. Having been informed by flight attendants of a “two-foot hole in the cabin ceiling” and of the injuries, the captain requested radar vectors to Yuma International Airport, the nearest suitable airport.
Examination of the airplane revealed an open flap of fuselage skin about 60 in (152 cm) long and 8 in (20 cm) wide at a lap joint near the top (crown) of the fuselage, adjacent to the trailing edge of the left wing. “The entire section of skin remained attached along the lower edge and was deformed outward,” the report said. “The fracture along the upper edge was through the lower [of three rivet rows] of the lap joint.”
The airplane had accumulated 48,748 hours and 39,786 cycles since its manufacture and delivery to the airline in 1996.
Investigators found that the fuselage crown skin had torn along 58 of the lower rivet holes. “Examination of the rivets in the fracture area revealed numerous anomalies,” the report said. Several rivets were oversized, some had no primer coating or only partial primer coating, and some had not been driven properly. None of the rivet holes in the lower fuselage skin were aligned with the holes in the doubler and the upper skin.
Three days after the accident, Boeing issued an alert service bulletin instructing 737 operators to inspect the affected lap joint for cracks. The bulletin subsequently was promulgated by the U.S. Federal Aviation Administration in an emergency airworthiness directive.
Takeoff Rejected for ‘Smoke’
Boeing 737-800. No damage. One serious injury, 15 minor injuries.
Shortly after beginning the takeoff from Glasgow (Scotland) Airport the morning of Oct. 19, 2012, the flight crew was informed by the cabin service director that an “urgent condition” existed in the cabin. The crew rejected the takeoff, stopped the 737 on the runway and initiated an emergency evacuation.
“The evacuation took an estimated 3 minutes and 38 seconds,” said the report by the U.K. Air Accidents Investigation Branch. “Passengers attempting to recover property from the overhead lockers delayed movement towards the exits, and the age or infirmity of some of the passengers may have extended the evacuation time.”
One of the 187 passengers was seriously injured and 15 others sustained minor injuries during the evacuation. “The injuries [were] due to passengers bumping into each other on the slides or being knocked to the ground,” the report said.
During the takeoff, cabin crewmembers and passengers had detected an unusual odor and had seen what they perceived as smoke emanating from the overhead lockers. “No source for the smoke was identified, but excessive moisture in the air conditioning system was identified as a possible factor,” the report said.
Due to a short taxi to the runway, the cabin was relatively warm and humid when the takeoff was initiated. Investigators determined that the “smoke” seen by the cabin occupants actually might have been mist created when a sudden influx of cold air entered the air conditioning system as engine power was increased for takeoff.
The report said that in the low lighting conditions in the cabin, the mist “could have given the appearance of smoke or fumes.”
Icing-Induced Stall on Final
Learjet 35A. Substantial damage. Two minor injuries.
The Learjet entered clouds at about 5,000 ft while descending to the Springfield, Illinois, U.S., airport the morning of Jan. 6, 2011. The flight crew noticed a trace accumulation of rime ice on the wing-tip fuel tanks and the windshield while being vectored by air traffic control for an instrument landing system (ILS) approach.
Nevertheless, the crew disengaged the anti-icing systems after establishing the airplane on the ILS glideslope. The copilot, who was flying the Learjet from the left seat, said that the airplane descended below the clouds shortly after intercepting the glideslope. “He recalled observing light frost on the outboard wing and tip tank during the approach,” said the NTSB report.
The airplane was on short final approach, and the pilot had just called out airspeed as 5 kt above the reference landing speed, when the stick shaker activated. The report said the Learjet stalled due to an accumulation of airframe ice.
The copilot applied full power, but the airplane touched down hard to the left of the runway centerline and then veered off the right side of the runway. The landing gear and the right tip tank separated before the airplane came to a stop in a grassy area. The pilot and one passenger sustained minor injuries; the copilot and the other three passengers were not hurt.
“The cockpit voice recorder transcript indicated that the pilots were operating in icing conditions without the wing anti-ice system activated for about 4 1/2 minutes prior to activation of the stick shaker,” the report said. “The airplane flight manual stated that even small accumulations of ice on the wing leading edge can cause an aerodynamic stall prior to activation of the stick shaker and/or stick pusher.”
Collision on Deice Pad
McDonnell Douglas MD-11F. Substantial damage. One minor injury.
Reduced visibility in blowing snow prevailed as the MD-11 flight crew was marshaled onto a deicing pad at Memphis (Tennessee, U.S.) International Airport the night of Dec. 26, 2012. “The crew taxied the airplane onto the pad in response to lighted wand signals” by the marshaler, the NTSB report said. “The operation was not using wing walkers.”
The first officer noticed two vehicles off the right side of the airplane that were parked outside the taxiway edge lines, but he could not see the MD-11’s wing tip through his window.
One of the pilots felt the freighter shudder at the same time the crew received a signal from the marshaler and a radio transmission from the deicing pad coordinator to stop taxiing. Neither pilot realized that the airplane had collided with a deicing vehicle.
The deicing pad coordinator radioed the crew to shut down the engines, and the airplane was towed back to the ramp.
The bottom of the right wing had struck the bucket on the deicing vehicle, which cracked the forward wing spar; damaged the outboard aileron and wing slats; and punctured the fuel tank, resulting in a leak of about 75 gal (284 L). A ground crewman in the deicing bucket sustained minor injuries.
Investigators found that the marshaler had not worked at the deicing pad previously and was not aware of a requirement to position MD-11s off the taxiway centerline to provide proper clearance. “The diagrams provided to the marshaler and coordinator were unclear and not sufficient to be standalone documents,” the report said.
NTSB determined that the probable cause of the accident was “the operator’s failure to provide appropriate training and documentation for ground personnel.”
Long, Fast Touchdown
Pilatus PC-12/45. Substantial damage. No injuries.
After completing several medevac flights, the flight crew and flight paramedic were returning to their home base in Timmins, Ontario, Canada, the night of Jan. 15, 2012, when engine anomalies occurred.
The single turboprop was at 15,000 ft and about 60 nm (111 km) from the airport when torque decreased, the low oil pressure and chip detector warning lights illuminated, and oil droplets struck the windshield.
“The flight crew reduced engine power, declared an emergency and requested a straight-in approach to Runway 10 at Timmins,” said the report by the Transportation Safety Board of Canada.
Airspeed was about 130 kt — about 46 kt higher than the appropriate speed for landing with full flaps — when the aircraft touched down about one-third of the way down the 4,907-ft (1,496-m) runway. The crew applied full wheel braking but then shut down the engine and feathered the propeller when they realized that they would not be able to stop on the runway.
The PC-12 overran the runway onto snow-covered terrain and slid to a stop about 1,200 ft (366 m) from the runway threshold. The wings and landing gear were substantially damaged, but the crew escaped injury.
Investigators found that the engine anomalies had resulted from the loss of oil after a B-nut detached from the oil outlet fitting on the torque limiter. The report noted that the B-nut lacked a secondary locking device, but why the nut loosened was not determined conclusively.
A contributing factor in the accident was that “the flight crew did not effectively manage the final approach and landing speed, resulting in the aircraft touching down long and fast and overrunning the runway,” the report said.
Engine Fire on Takeoff
ATR 72. Substantial damage. No injuries.
The airplane was departing from St. Croix, U.S. Virgin Islands, with 44 passengers and four crewmembers the night of Jan. 11, 2010, when the flight crew received warnings of a fire in the left engine. The pilot declared an emergency, shut down the engine and discharged a fire bottle.
The fire warnings continued after the pilot discharged the second bottle. “The pilot performed an air turn-back and landed the airplane uneventfully approximately 11 minutes later,” the NTSB report said.
Investigators found a substantial fuel leak at the no. 2 fuel nozzle manifold. Further examination of the engine revealed two manufacturing defects at the fuel nozzle manifold adapter.
“The first defect, poor surface finish, caused damage to the transfer tube O-ring during the installation process, initiating an internal fuel leak,” the report said. “The second defect, blockage of the internal safety tell-tale drain due to an improper machining and subsequent cleaning procedure, prevented the leaking fuel from flowing into the tell-tale drain and being detected by maintenance personnel.”
Gambling on a Tailwind
Piper Chieftain. Substantial damage. Three fatalities, one serious injury, one minor injury.
The Chieftain was on a medevac flight from Palm Beach, Florida, U.S., to Chicago Executive Airport near Wheeling, Illinois, the night of Nov. 28, 2011, and had made a refueling stop in Jessup, Georgia. Aboard the airplane were the patient and his wife, a medical crewmember, a pilot-rated passenger and the pilot.
Noting that records showed the engines had been consuming more fuel than normal, the NTSB report said that the airplane did not have enough fuel to complete the flight from Jessup to Wheeling. “However, a 20-kt tailwind was predicted, so it is likely that the pilot was relying on this to help the airplane reach the airport.”
Chicago Executive Airport had 10 mi (16 km) visibility and a 1,400-ft overcast ceiling. As the Chieftain was being vectored for the ILS approach to Runway 16, the right engine’s low-fuel-flow warning light illuminated. The pilot switched from the auxiliary fuel tank to the main tank, and the light went out.
The pilot requested a vector direct to the ILS outer marker, but the controller declined the request. At this time, the warning light illuminated again, and the pilot began to cross-feed fuel from the left main tank to the right engine. The light went out but illuminated again shortly thereafter.
The pilot declared an emergency and told the controller that he was heading directly toward the airport. Both engines then lost power, and the pilot feathered the propellers. He radioed that he was “out of fuel” and that the airplane was “coasting.”
When the Chieftain descended below the clouds, the pilot reported that he had the airport in sight and was cleared for a visual approach to Runway 16. However, the airplane struck trees and crashed in a residential area about 3 nm (6 km) northeast of the airport. The two passengers and the pilot were killed, the pilot-rated passenger was seriously injured, and the medical crewmember sustained minor injuries.
NTSB concluded that the probable causes of the accident were “the pilot’s inadequate preflight planning and in-flight decision making.”
“It is likely that, had the pilot monitored the gauges and the consumption rate for the flight, he would have determined that he did not have adequate fuel to complete the flight,” the report said.
Toxicological tests revealed that the pilot had used marijuana. This was ascribed by NTSB as a contributing factor in the accident. “The level of impairment could not be determined based on the information available,” the report said. “However, marijuana use can impair the ability to concentrate and maintain vigilance, and can distort the perception of time and distance.”
Faulty Heater Causes Fire
Cessna 401. Destroyed. Four fatalities, one serious injury.
The 401’s cabin heater had been found to be inoperative during an annual inspection of the airplane in January 2011. A work order completed a month later indicated that the combustion heater operated normally after maintenance was performed on the fuel safety valve and airflow switch.
However, “there was no logbook entry that returned the heater to service, [and] there were no entries in the maintenance logbooks that documented any testing of the heater or tracking of the heater’s hours of operation,” the NTSB report said.
The report noted that an airworthiness directive issued in 1981 requires inspection of the cabin heater every 250 hours and overhaul of the heater every 1,000 hours.
A flight instructor told investigators that the overheat warning light had illuminated during an instructional flight in April 2012, and that the cabin heater had shut down automatically. “The flight instructor showed the pilot how to reset the overheat circuit breaker,” the report said.
Although the airplane flight manual states that the cause of an overheat should be determined and fixed before further flight, there is no record of maintenance on the cabin heater before the pilot departed with four passengers from Tulsa, Oklahoma, U.S., for a flight to Council Bluffs, Iowa, the afternoon of May 11, 2012.
The 401 was in visual meteorological conditions at 8,000 ft when the pilot turned on the cabin heater. A passenger later told investigators that a “terrible smell” was detected and that when the pilot turned off the heater, dark, black smoke filled the cabin, making it difficult to see.
“In an attempt to extinguish the fire, they poured water bottles in the vents, which had no effect,” the report said. “The pilot quickly descended.” During the emergency landing, the right wing struck the ground, and the airplane cartwheeled into a tree line between two farm fields.
Examination of the cabin heater revealed several leaks around weld points on the combustion chamber.
Disorientation on a Dark Night
Aerospatiale AS350-BA. Substantial damage. Three fatalities.
The pilot and two medical crewmembers had transported a patient to Reno, Nevada, U.S., and were returning the medevac helicopter to its base in Susanville, California, on Nov. 14, 2009. The NTSB report said that on a previous flight, the pilot had followed a highway to Susanville and had flown at 8,500 ft to clear mountain tops along the route.
After departing from Reno at 0143 local time, the medical crew made position reports every 10 minutes to the dispatch center. The last position report was made at 0153, when the helicopter was 43 nm (80 km) southeast of Susanville. “At 0201, dispatch received a transmission that the helicopter was going down,” the report said.
A witness who was driving on the highway near Doyle, California, saw the helicopter flying straight and level before it entered a rapid descent. The witness momentarily lost sight of the AS350 but then saw a fireball. “On-site documentation of the wreckage suggested that the helicopter was in a nose-low attitude and about a 90-degree bank angle when it contacted the ground,” the report said.
NTSB determined that the pilot likely had become spatially disoriented while maneuvering in darkness to avoid clouds and had lost control of the helicopter. Broken ceilings, with cloud tops at 13,000 ft, and moderate icing conditions had been reported in the area.
External Load Snags Tower
MD Helicopters 500E. Substantial damage. One fatality, one serious injury, two minor injuries.
The pilot maneuvered the helicopter near a transmission tower in Thomas, West Virginia, U.S., the morning of Oct. 30, 2010, to pick up three linemen who were working on the tower. The linemen secured their equipment to a grappling hook on a 50-ft (15-m) external line before boarding the helicopter. Two linemen sat in the cabin, the third stood on the left skid.
“As the pilot attempted to maneuver the helicopter clear of the tower, it paused and then began to shake,” the NTSB report said. The helicopter then struck wires and descended to the ground. The lineman on the skid was killed, the pilot was seriously injured, and the other two linemen sustained minor injuries.