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.
Thrust Reverser Inoperative
Airbus A310-324. Destroyed. Thirty fatalities.
Forgoing the use of autobrakes for landing on a wet runway, a prolonged flare and an inoperative thrust reverser were among the factors that led to the overrun and fire that killed 29 passengers and one cabin crewmember at Khartoum the night of June 10, 2008, according to the Sudanese Air Accident Investigation Central Directorate (AAICD). The directorate’s final report, which also cited a substantial but unnoticed wind shift shortly before touchdown, was posted recently by the French Bureau d’Enquêtes et d’Analyses (BEA).
The accident occurred during a trip from Cairo, Egypt, to the airline’s home base in Khartoum, with stops in Amman, Jordan, and Damascus, Syria. The captain, 60, had 14,180 flight hours, including 3,088 hours in type. The copilot, 50, had 9,879 flight hours, with 3,347 hours in type. Both pilots held several type ratings, and they had been off duty more than 24 hours before the trip began.
Two months earlier, the thrust reverser on the A310’s left engine did not stow after landing, and the master actuator was replaced. However, the thrust reverser again failed to stow on command the day before the accident flight. The reverser was deactivated and secured in the stowed position according to the provisions of the A310’s minimum equipment list pending further corrective maintenance.
The flights to Amman and Damascus proceeded without incident. On the last leg, however, the flight crew was unable to land at Khartoum as scheduled because of thunderstorm activity at the airport. The crew diverted the flight to Port Sudan, where the A310 was refueled. The aircraft was on the ground about 75 minutes before the crew decided to complete the flight to Khartoum, where weather conditions reportedly were improving.
As the A310 neared Khartoum, the crew received the latest meteorological report, which indicated that the surface winds were from 360 degrees at 12 kt and that runway visual range was 6,000 m (4 mi) in heavy rain.
The instrument landing systems at Khartoum were out of service, and the crew was cleared for the VOR/DME (VHF omnidirectional range/distance-measuring equipment) approach to Runway 36, which was 2,980 m (9,777 ft) long and 45 m (148 ft) wide.
“The captain was flying the aircraft,” the report said. “He complied with the control clearances and performed a stabilized approach. The CVR [cockpit voice recorder] reading showed good coordination between the captain and the copilot.”
As the crew configured the aircraft for landing, the copilot “suggested the use of autobrake, and the captain decided not to use it,” the report said. The reason for this decision was not specified.
The captain disengaged the autopilot as the aircraft descended through 800 ft. The airport traffic controller had advised the crew that the winds were from 320 degrees at 7 kt and that the runway was wet. However, as the A310 neared the runway, the wind shifted to the south and increased in velocity.
“Just before touchdown, the FDR [flight data recorder] recorded 140 kt for indicated airspeed and 155 kt for groundspeed,” the report said. “This means that the aircraft was actually subject to a 15-kt tailwind component. The crew seemed not to have realized it. Due to the tailwind, the aircraft touched down about 850 to 900 m [2,789 to 2,953 ft] from the threshold. A smooth landing was recorded, which might also be a contributing explanation for such a long distance.”
The ground spoilers deployed normally on touchdown, and the captain moved both thrust levers to the full-reverse position. With only the right engine producing reverse thrust, the aircraft veered right. The captain moved the thrust levers back to the idle position and used differential manual braking to return the aircraft to the runway centerline.
The aircraft was about 80 m (262 ft) from the end of the runway when the captain again applied reverse thrust, “but the speed was too low for this action to be efficient,” the report said. Rubber marks on the runway indicated that all the wheels were locked by the brakes as the aircraft neared the end of the runway, but there was no sign of hydroplaning.
“Thirty-six seconds after touchdown, the aircraft overran Runway 36 at 76 kt,” the report said. The A310 rolled 215 m (705 ft) on hard, rough sand, struck several lights and antennas, and crossed a ditch before stopping.
A fuel-fed fire erupted near the right wing root after the aircraft came to a stop. “The investigation revealed that the fire could not be fought by the airport fire department with the required rapidity and efficiency,” the report said. “This was due to training as well as communications and infrastructure issues.”
The evacuation was impeded by thick smoke that rapidly spread through the cabin and by some passengers who attempted to retrieve carry-on items. The causes of the fatalities were not specified. The survivors — 177 passengers and 10 crewmembers — used the left forward slide to exit the aircraft before it was consumed by fire.
Based on the findings of the investigation, the AAICD made several recommendations to the Sudanese Civil Aviation Authority, including improving airport firefighting and wind-reporting capabilities, and establishing means for measuring and reporting runway friction levels.
Flight Bag Foibles
Boeing 737-300. Substantial damage. No injuries.
A mistake in the calculation of takeoff performance data and a malfunctioning flight control system led to a premature and excessive rotation that resulted in a tail strike on takeoff from Chambéry (France) Airport the morning of April 14, 2012. The accident caused damage to the 737’s rear fuselage skin and frames, but there were no injuries to the 131 passengers and five crewmembers.
Investigators found that the commander had not revised the aircraft’s takeoff weight while using a portable electronic flight bag (EFB), resulting in airspeeds and a thrust setting that were erroneously low.
“The investigation also revealed wider issues relating to the general design and use of EFB computers to calculate performance data,” said the report by the U.K. Air Accidents Investigation Branch (AAIB).
The 737 had been flown with no passengers aboard to Chambéry from London earlier that morning. When the commander used the EFB to calculate takeoff performance data for the return trip to London, he neglected to enter the takeoff weight shown on the load sheet. The EFB reverted to the takeoff weight that had been entered before the departure from London, which was 6,600 kg (14,550 lb) lower than the actual takeoff weight at Chambéry. Consequently, the calculated rotation speed of 127 kt was 12 kt lower than it should have been, and the reduced thrust setting of 88.6 percent was 4.2 percent too low.
“Both pilots stated that they would normally cross-check the performance figures once they had been calculated on the EFB,” the report said. “However, on this occasion, and for reasons the pilots could not recall, this was not done.”
The subsequent early rotation was exacerbated by a broken spring in the aircraft’s elevator feel and centering unit, which caused “reduced resistance in the flight controls in pitch, contributing to the excessive pitch attitude achieved during rotation,” the report said.
The flight crew and a flight attendant felt a “judder” during takeoff, but this was attributed by the pilots to turbulence. The remainder of the flight to London Gatwick Airport was uneventful. After shutting down the engines, the pilots were informed by ground personnel that the rear fuselage was damaged.
The operator of the 737 told investigators that all company pilots had been trained and checked on the use of the EFB. “However, the investigation revealed a lack of clarity in the way the procedures were laid out and on details of how information should be checked,” the report said.
The report cited “a number of previous incidents and accidents resulting from incorrect calculation of takeoff performance,” including the fatal crash of a 747 freighter in Halifax, Nova Scotia, in October 2004, which also involved calculations based on an erroneously low takeoff weight that had been retained in an EFB (ASW, 10/06).
The report (EW/C2012/04/03 in AAIB Bulletin 4/2013) discusses efforts by Australian, European and North American authorities to reduce errors in performance-data calculations using EFBs but said, “There remains … a continued vulnerability to the use of incorrect data in making these calculations, a solution to which remains outstanding. This accident serves to demonstrate that, given these circumstances, the existence of and adherence to robust procedures, and appropriately designed software and hardware, are essential.”
The investigation prompted the AAIB to reiterate recommendations for establishing means to gauge the progress of a takeoff once it has begun: “This event once again emphasises the need for technical solutions for takeoff performance monitoring, to cater for those occasions where current safeguards have failed.”
Airbus A319-112. No damage. One serious injury, two minor injuries.
The A319 was on initial descent to land at Fort Lauderdale the afternoon of May 10, 2012, when the flight crew “noticed typical Florida summertime cumulus cloud conditions,” said the report by the U.S. National Transportation Safety Board (NTSB).
The captain told the flight attendants that he would illuminate the seat belt sign early because of expected turbulence and instructed them to complete the initial cleanup of the cabin early and to be seated when the seat belt sign illuminated.
The captain illuminated the seat belt sign as the airplane descended through 25,000 ft. The A319 subsequently was descending through 12,400 ft when it encountered turbulence. The forward flight attendant, who was securing the galley, sustained serious leg injuries when she was thrown to the floor, and two other flight attendants suffered minor injuries. None of the 138 passengers was hurt. The report noted that the turbulence encounter occurred about 20 minutes after the captain briefed the flight attendants.
The seriously injured flight attendant was aided by medically qualified passengers, including a surgeon. “The flight crew advised ATC [air traffic control] that they had an injured crewmember and requested priority handling and for paramedics to meet the airplane on arrival,” the report said. “The ATC approach controller did not forward the request for paramedics. The crew also attempted to contact the company station agents and dispatch, but received no response.
“The lack of ATC coordination and lack of company personnel to monitor communications from inbound flights delayed the arrival of emergency medical personnel to meet the flight.”
Minimum Fuel on Go-Around
British Aerospace 146. No damage. No injuries.
The aircraft was en route with 40 passengers and four crewmembers from Paris to Zurich, Switzerland, the night of June 17, 2010. However, the flight crew was unable to land the 146 in Zurich because of thunderstorms and heavy rain.
“Given the immediate forecast and the absence of an estimated time for a new approach, the crew decided to divert to the diversion aerodrome, Basel-Mulhouse-Freiburg, without holding at Zurich,” said the BEA report. “The remaining fuel quantity was about 2,170 kg [4,784 lb], which corresponded to about 75 minutes of flight at cruising speed.” The Basel-Mulhouse-Freiburg Airport, which is jointly operated by France and Switzerland, is about 41 nm (76 km) northeast of Zurich.
“While receiving vectors for the instrument landing system (ILS) approach to Runway 33, the crew asked for a shortened flight path, without giving any reason,” the report said. The 146 was on final approach when the airport traffic controller cleared the crew of an Airbus A319 for takeoff from Runway 33. The clearance was in French and was not understood by the English-speaking crew of the 146.
The aircraft was about 5 nm (9 km) from the runway when the crew saw the A319 on the runway and asked the controller to confirm that they were cleared to land. The controller responded “negative,” told the crew to continue the approach and advised that the A319 was departing from Runway 33.
Although the aircraft’s fuel supply was at the level at which the operator requires pilots to declare an urgency, the crew did not. Consequently, the controller was not aware of the 146’s fuel state.
The 146 was about 2 nm (4 km) out and the A319 was still on the runway when the controller told the Airbus crew to stop and asked the 146 crew to go around. “The latter [initially] refused because they did not have enough fuel and requested that the A319 vacate the runway,” the report said.
The controller then ordered the 146 crew to go around. The crew complied with the instruction and said, “We are declaring a fuel emergency now. We request priority vectors for landing.” They landed the aircraft about eight minutes later, after receiving vectors for a visual approach. “On the ground, the quantity of fuel remaining was 1,220 kg [2,690 lb],” the report said.
The report concluded that the incident was caused by “the late communication by the crew to ATC of their low fuel situation and their emergency situation.” Based on the investigation, BEA recommended that the European Aviation Safety Agency adopt the International Civil Aviation Organization (ICAO) provision of declaring “minimum fuel” when a flight crew can accept little or no delay at the destination.
“The notion of minimum fuel defined by ICAO allows a crew to describe to the air traffic services a potentially critical situation during a diversion while avoiding the declaration of a distress or emergency situation,” the report said.
‘Confused Crew Coordination’
De Havilland Twin Otter. Destroyed. Two fatalities, four serious injuries, three minor injuries.
The float-equipped aircraft was on left base to land at the floatplane base in Yellowknife, Northwest Territories, Canada, the morning of Sept. 22, 2011, when the traffic controller at the nearby airport advised the flight crew that the winds were variable from the southwest at 10 kt, gusting to 30 kt.
The first officer (FO) was flying from the right seat. “Due to the 2- to 3-ft waves (rollers) on the lake, the crew planned their approach so as to land close to the shore,” said the report by the Transportation Safety Board of Canada (TSB). “The captain also advised that the airspeed should be kept above 80 kt indicated airspeed (KIAS), which is 10 KIAS above the normal approach speed [for a full-flap approach]. During final approach, on a track of 195 degrees, the captain cautioned the FO twice about the airspeed getting too low.”
The Twin Otter bounced on touchdown and contacted the water again in a right-wing-low attitude. “The [right] float dug in, and the aircraft yawed to the right, turning towards the shore,” the report said. “Without declaring that he was taking control, the captain placed his right hand on the power lever over the FO’s left hand and initiated full power for a go-around.”
The aircraft continued to turn right at low airspeed and in a nose-high, right-wing-low attitude. The captain called for the flaps to be retracted shortly before the right wing struck power lines, causing the aircraft to pitch nose-down. The floats then struck the side of an office building, and the Twin Otter crashed in a parking lot. Both pilots were killed and all seven passengers were injured, but no one on the ground was hurt.
The TSB concluded that the bounced landing had been caused by airspeed fluctuations and the gusty crosswind conditions, and the loss of control had resulted from improper go-around techniques. “It is possible that confused crew coordination during the attempted go-around contributed to the loss of control,” the report said.
Magnetic Anomalies Affect HSIs
Piaggio P180 Avanti. No damage. No injuries.
Vsual meteorological conditions (VMC) prevailed when the Avanti took off from Runway 27 at London City Airport and began a right turn to the assigned easterly heading the evening of April 26, 2012. The aircraft was at 3,000 ft when the radar controller noticed that it was heading southeast, toward the path of an Avro RJ-85 that was on final approach to Runway 27.
The controller told the Avanti crew to turn left to a heading of 030 degrees. “This was acknowledged but was apparently not complied with, so a further instruction to turn left was made using the phrase ‘avoiding action’ and with details of the conflicting traffic,” the AAIB report said.
Suspecting that the Avanti crew had a navigation problem, the controller told them to climb to 4,000 ft and to turn left until advised to discontinue the turn. During the turn, the Avanti came within 2.7 nm (5.0 km) laterally and 700 ft vertically of the RJ-85. The controller told the Avanti crew to stop the turn at a radar-indicated heading of 060 degrees. The crew reported that their indicated heading was northerly. After resetting their horizontal situation indicators (HSIs), the crew continued the flight without further incident.
Investigators found that the crew had selected the directional gyro (DG) mode while adjusting the HSIs to match the runway heading and then had selected the slaved mode before takeoff. “The heading reference system should normally be kept in its slaved mode for normal operations and DG mode [only should be] used in case of failure of the slaved system,” the report said.
The report noted that the crews of several other aircraft also had experienced significant navigational problems after taking off from London City Airport (ASW, 5/08). “It was established that local magnetic anomalies in the area of the runway holding point could adversely affect cockpit heading indications and, in some cases, lead to heading system failure indications,” the report said.
Maintenance Check Neglected
ATR 72-202. No damage. No injuries.
Routine maintenance at Edinburgh, Scotland, was completed nearly five hours after the flight crew was scheduled to depart for a positioning flight to Paris the afternoon of March 15, 2011. A post-maintenance functional flight check apparently was not conducted before the crew took off in night VMC.
The crew maintained 170 kt during the climb to Flight Level 230 (approximately 23,000 ft). “As the aircraft levelled and accelerated through about 185 kt, the crew felt it roll to the left by about 5 to 10 degrees, and they noticed that the slip ball was indicating fully right,” the AAIB report said.
The copilot, the pilot flying, disengaged the autopilot and applied right rudder and right aileron to regain directional control. “He reported that the rudder pedals felt unusually ‘spongy’ and that the aircraft did not respond to his rudder inputs,” the report said. “He had to maintain 15 to 20 degrees of right bank to hold a constant heading.”
A flight control warning light illuminated, indicating a fault with the rudder travel limitation unit (TLU). The commander declared an urgency and requested vectors from ATC to return to Edinburgh. “The copilot assessed that he had very little control authority to make right turns, so the commander requested that only left turns be given,” the report said. Control became more difficult as airspeed decreased, but the pilots were able to land the ATR at Edinburgh.
Investigators found that one of the cams on the rudder TLU mechanism had been reinstalled incorrectly and had restricted rudder control excessively, resulting in the uncommanded left roll as airspeed increased to 185 kt.
“The required independent inspection of the work and the operational test of the TLU system were not carried out,” the report said. “Commercial pressure was identified as the most significant factor which influenced the decision to perform unapproved and unrecorded maintenance on the TLU system.”
Stall After Engine Shutdown
Cessna 421C. Substantial damage. Four fatalities.
Shortly after the 421 lifted off from Joe Foss Field in Sioux Falls, South Dakota, U.S., for a charter flight the afternoon of Dec. 9, 2011, the airport tower controller told the pilot that a plume of smoke was visible behind the airplane. Other witnesses saw white smoke and flames emerging from the inboard side of the left engine.
The pilot did not acknowledge the controller’s advisory but began a left turn, apparently in an attempt to return to the runway. The smoke and flames disappeared shortly before the 421 pitched nose-down and descended to the ground.
“A postaccident examination determined that the left engine fuel selector and fuel valve were in the ‘OFF’ position, consistent with the pilot shutting down that engine after takeoff,” the NTSB report said. “However, the left engine propeller was not feathered [and] the landing gear and wing flaps were extended at the time of impact.”
Initial examination of the wreckage revealed that the oil cap on the left engine was not secured; however, the report said that this might have resulted from the impact and subsequent fire. Investigators determined that the right engine was producing power on impact. Subsequent disassembly and inspection of the left engine revealed nothing that would have caused a loss of power.
The report said that the probable cause of the accident was “the pilot’s failure to maintain adequate airspeed after shutting down one engine, which resulted in an aerodynamic stall and impact with terrain.” A contributing factor was his nonadherence to single-engine emergency procedures that included feathering the propeller and retracting the landing gear and flaps.
Engine Cylinder Separates
Britten-Norman Trislander. Substantial damage. No injuries.
The aircraft was cruising at 5,000 ft during a scheduled flight with seven passengers from Alderney, Channel Islands, to Southampton, England, the morning of March 27, 2012, when the pilot heard a very loud bang and felt severe vibration. He determined that the no. 2 (tail-mounted) engine had failed.
“The pilot selected full power on the no. 1 and no. 3 engines, and advised ATC of his intention to return to Alderney,” the AAIB report said. “While carrying out the engine failure checklist, the pilot was unable to operate the no. 2 propeller lever through its feather gate, which left the no. 2 propeller unfeathered and ‘windmilling.’”
Unable to maintain altitude, and with a sink rate of 200 fpm, the pilot declared an emergency. “At some point during the descent, the propeller blades on the no. 2 engine moved to the feather position [and] stopped rotating,” the report said. “The pilot was subsequently able to control the rate of descent.” He landed the Trislander at Alderney without further incident.
Investigators found that corrosion and fatigue cracking had caused a cylinder mounting stud on the no. 2 engine to fail, resulting in the cylinder’s separation from the crankcase. The damage distorted a cable guide conduit that disabled the manual propeller-feathering system; the propeller eventually feathered when engine oil pressure decreased due to oil leaking through the hole in the crankcase.
Fuel Flow Blocked
Cessna 402. Substantial damage. Two minor injuries.
Shortly after the landing gear was retracted during departure for a skydiving flight from Caldwell, Idaho, U.S., the afternoon of June 20, 2011, the right engine lost power, and the pilot decided to reject the takeoff.
“Because the airplane was at a very low altitude, the pilot was not sure that all three landing gear would fully extend before the airplane touched down,” the NTSB report said. “Therefore, he elected to keep the landing gear retracted, and the airplane touched down on the soft, rough terrain adjacent to the runway.” The pilot and one passenger sustained minor injuries; the other seven passengers were not hurt.
Examination of the right engine revealed nothing that could have caused the power loss, but three pieces of polyisoprene (synthetic rubber) were found in the tank supplying fuel to the engine. “Each individual piece was large enough to plug the orifice to the fuel boost pump, and it is likely that one or more of the pieces interrupted the fuel flow to the engine and resulted in the loss of power,” the report said. “It was not determined when or how the material had entered the fuel tank.”
‘Focused on the Mission’
Bell OH-58A. Substantial damage. One minor injury.
The law enforcement helicopter had been dispatched to aid in the search for a person who was ejected from a motor vehicle during a roll-over accident on a highway near Fort Pierce, Florida, U.S., the afternoon of May 29, 2011.
The pilot was maneuvering the helicopter at about 400 ft above the ground when an uncommanded right yaw developed. He attempted to stop the rotation, but the Kiowa entered an uncontrolled descent to the ground.
“The pilot stated that he was more focused on the mission than on flying the helicopter,” the report said. “He lost awareness of the wind condition and did not recognize the possibility of a loss of tail rotor effectiveness.”
Power Loss Leads to Ditching
Bell 206L-3. Destroyed. One minor injury.
The pilot had departed from Maungakaramea, in northern New Zealand, to check fishing conditions in Bream Bay the afternoon of Jan. 20, 2011. He was cruising at 110 kt and about 1,000 ft above the bay when the engine surged and rotor speed began to decrease.
“The pilot immediately entered autorotation to preserve main rotor rpm,” said the report by the New Zealand Transport Accident Investigation Commission. He attempted unsuccessfully to restore power before ditching the helicopter in the bay. The LongRanger, which did not have flotation gear, rolled inverted and sank in less than 15 minutes.
The pilot began to swim toward the shore. He was in the water more than two hours without a life vest and suffered hypothermia and fuel burns before being rescued by a helicopter crew that had been alerted by witnesses.
Too Rich, Too High
Robinson R44. Substantial damage. No injuries.
A flight instructor and a commercial pilot were ferrying the R44 to its new owner the morning of May 10, 2012. The helicopter was at 10,000 ft over mountainous terrain near Grants, New Mexico, U.S., when the instructor decided to conduct a practice autorotation.
“During the autorotation, the engine stopped producing power … due to an excessively rich fuel mixture,” the NTSB report said. “The instructor continued the autorotation, [and] during the landing, the main rotor blades severed the tail boom.”