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.
Radar Was Inoperative
Airbus A319s. No damage. One minor injury.
An unreliable air traffic control (ATC) radar system necessitating the use of ATC procedures that were unfamiliar to some controllers, as well as thunderstorms prompting course deviations were among the factors that created a high-stress, high-workload environment in which a trainee controller issued instructions that placed converging A319s at the same alti-tude near the Basel Mulhouse airport in Switzerland the evening of June 29, 2010.
A collision was averted when the flight crews complied with resolution advisories (RAs) generated by their traffic-alert and collision avoidance systems (TCAS). However, a cabin crewmember was slightly injured during abrupt maneuvering by the crew of one aircraft.
The English translation of the final report on the serious loss of ATC separation, published by the Bureau d’Enquêtes et d’Analyses (BEA) in May, said that the radar system problems had originated a few months earlier, when the Basel Mulhouse approach control facility was assigned the responsibility for coordinating air traffic in additional airspace transferred from an adjacent facility.
The central processing units in the Basel Mulhouse facility’s computers did not have sufficient capacity to handle the additional traffic. The result was serious display malfunctions that led to the radar system being declared inoperative three days before the incident.
“For three days, air traffic control at Basel Mulhouse had been based on ‘procedures’ [which were not defined in the report] because of uncertainty about the reliability of the radar display,” the report said.
The trainee controller and his instructor had not previously used procedural control methods. And, although the radar system had been declared inoperative, they had their radar display on when the incident occurred. “The simultaneous use of procedural control and an uncertain radar image increased the workload of the controllers and may have helped create confusion about the positions of the aircraft,” the report said.
One of the A319s, of French registry, had departed from Runway 15 at the Basel Mulhouse airport for a scheduled flight to Paris and was climbing westbound. The other aircraft, of Swiss registry, was inbound on a flight from Palma, Spain, and was southwest of the airport, descending to land.
The flight crews of both aircraft had requested and received clearance to deviate around thunderstorm cells. The A319s were on converging courses, and the trainee controller had planned to resolve the conflict by instructing the crew of the French aircraft to stop their climb at 10,000 ft and to tell the crew of the Swiss aircraft to stop their descent at 11,000 ft. However, when he issued the instructions within a period of one minute, he inadvertently assigned both aircraft the same altitude: 11,000 ft.
The report said that the trainee believed he had assigned 10,000 ft to the crew of the French aircraft. He did not detect the error when the crew read back the faulty clearance. The trainee’s instructor, who was handling additional duties at the time, also did not detect the error.
Several factors complicated the situation. The French aircraft was climbing at 3,000 fpm, which the report called “ex-cessive.” In addition, TCAS traffic advisories were generated aboard both aircraft at the same time a short-term conflict alert was generated in the approach control facility.
The trainee reacted to the alert by telling the crew of the French aircraft to stop climbing at 10,000 ft. However, the aircraft already was climbing through 10,600 ft when the pilot flying (PF) disengaged the autopilot and applied a nose-down pitch input in response to the trainee’s instruction. Simultaneously, a TCAS “maintain vertical speed” RA was generated aboard the French aircraft. The PF changed from a nose-down to a nose-up pitch control application.
While this was happening, a “monitor vertical speed” RA was generated aboard the Swiss aircraft. The report said that this RA prompted the crew not to climb. However, the PF inadvertently applied a nose-up pitch input while disengaging the autopilot, then applied a nose-down input, changing the pitch attitude from 5.3 degrees nose-up to 5.6 degrees nose-down.
A series of coordinated, corrective RAs then were generated aboard both aircraft. The French aircraft crew received a “descend, descend now” RA while the Swiss aircraft crew received a “climb, climb now” RA.
The report said that the flight control inputs by the pilot of the Swiss aircraft were more abrupt than necessary. “During these manoeuvres, the vertical load factor recorded on [the Swiss aircraft] oscillated between – 0.19 g and 2.04 g,” the report said. “The minor injury to [the] cabin crewmember was due to the abrupt manoeuvres.”
The A319s came within 0.29 nm (0.53 km) horizontally and 1,760 ft vertically of each other before the flight crews received TCAS “clear of conflict” messages.
The BEA concluded that “the loss of separation that characterized this serious incident was due to an error in speech by the trainee controller … and the non-detection of that error by the instructor controller.”
The investigation led to several recommendations, including that the French ATC authority issue clear instructions on the use of radar imagery when it is known to be unreliable or when procedural control is in use, and that the International Civil Aviation Organization study the feasibility of incorporating TCAS resolution maneuvering in aircraft autoflight sys-tems.
Fire Traced to Loose Nut
Embraer 190-100. Minor damage. Eight minor injuries.
A fire erupted in the no. 1 engine cowling as the airplane was rolling out on landing at Nassau (Bahamas) International Air-port on Sept. 3, 2009. The flight crew shut down the engine and pulled the fire handle.
Eight of the 84 passengers sustained minor injuries during the subsequent emergency evacuation, said the report by the U.S. National Transportation Safety Board (NTSB).
Investigators traced the fire to a B-nut that had been cross-threaded on a fuel-supply coupling during the original as-sembly of the General Electric CF34 engine. The improperly seated nut prevented engagement of a metal seal in the high-pressure fitting, leaving an O-ring to act as the primary seal until it failed, causing fuel to be sprayed into the cowling.
Anomalies Prompt Diversion
British Aerospace 146-300. No damage. No injuries.
Shortly after departing from Exeter (England) Airport for a cargo flight to Belgium the night of Sept. 19, 2013, the flight crew saw the “Freight Door Unlocked” warning light illuminate and then heard loud noises emanating from the main cargo area.
“The pilots suspected that the two indications were connected and that the aircraft had suffered structural damage,” said the report by the U.K. Air Accidents Investigation Branch (AAIB). They declared an emergency, diverted to London Gatwick and landed without further incident.
Investigators found that the anomalies were not related. The warning light was triggered by a freight door latch proximi-ty switch that was out of adjustment. “The noises were probably caused by a flexible duct in the air conditioning bay be-coming detached,” the report said.
‘Inadequate Route Planning’
Beech King Air C90GT. Substantial damage. One fatality.
After deplaning passengers at Nemacolin Airport in Farmington, Pennsylvania, U.S., the morning of June 22, 2012, the pilot departed for a visual flight rules (VFR) positioning flight to Morgantown (West Virginia) Municipal Airport, about 20 nm (37 km) southwest, to refuel the airplane.
“The pilot had chosen a direct flight route near rising terrain and obstructions within a designated mountainous area at his selected cruise altitude of 3,100 feet, which was below the published maximum elevation figure of 3,500 feet depicted on the VFR sectional chart for the area,” the NTSB report said.
The King Air was at 3,100 ft when the pilot established radio communication with an approach control facility. The con-troller assigned a transponder code and advised the pilot that the airplane was in radar contact.
The King Air was about 9 nm (17 km) from the Morgantown airport when the pilot descended to 3,000 ft. Shortly thereafter, the airplane struck a 3,089-ft communications tower and descended to the ground.
“Aeronautical charts found on board the airplane depicted the tower hazard, so the pilot should have had some aware-ness of the tower’s presence,” the report said, noting that the collision might have occurred in instrument meteorological conditions. A witness near the accident site described the weather as “cloudy with lightning and thunder.”
Investigators found that the terrain-inhibit mode for the airplane’s enhanced ground-proximity warning system (EGPWS) had been engaged. This prevented the system from generating any visual or aural warnings.
NTSB concluded that the pilot’s “inadequate preflight route planning” was the probable cause of the accident and that contributing factors were his improper use of the EGPWS and the controller’s “failure to issue a safety alert regarding the proximity of the tower.”
EFIS Goes Blank on Go-Around
Jetstream 41. No damage. No injuries.
The aircraft was on final approach to Wick (Scotland) Airport the morning of Sept. 24, 2013, when the flight crew lost visual reference with the runway. “During the missed approach, momentary blanking of the electronic flight instrument system (EFIS) displays occurred, but the standby instruments continued to operate normally,” the AAIB report said.
During the second approach, the copilot’s displays went blank, and the crew decided to divert to Aberdeen Airport, where the weather was better. “During the diversion, VHF communication difficulties were experienced, but the aircraft landed with-out further incident,” the report said.
Investigators found that the avionics problems had been caused by unrelated faults. The blanking of the copilot’s EFIS displays and the VHF communications difficulties were caused by a loss of electrical power to the right essential bus bar. The transient blanking of the pilot’s displays was caused by the failure of transzorbs, which are installed in the windshield heating system and designed to protect avionics equipment from static.
‘Don’t Pitch Up’
Cessna 208B. Destroyed. One fatality.
Cessna 207. Substantial damage. No injuries.
The Caravan and the 207, operated by different charter companies, departed about the same time from neighboring remote villages for positioning flights on similar routes to Bethel, Alaska, U.S., the afternoon of Sept. 2, 2011.
“While en route, the Cessna 207 pilot talked with the Cessna 208B pilot on a prearranged radio frequency, and the two agreed to meet up in flight for the return to their home airport,” the NTSB report said.
The 207 pilot told investigators that she was in cruise flight at 1,200 ft when the Caravan flew into position on the left side. “Then, unexpectedly and unannounced, the pilot of the Cessna 208B maneuvered his airplane above and over the top of her airplane,” the report said.
The 207 pilot radioed that she could not see the Caravan and was concerned about its position. The Caravan pilot re-plied, “Whatever you do, don’t pitch up.” She then saw the Caravan’s wings and cockpit on the right side of the 207 and felt an impact with the right wing.
The Caravan descended steeply in a nearly vertical nose-down pitch attitude and struck terrain near Nightmute, Alas-ka. The 207 pilot was unable to maintain level flight and conducted an emergency landing on the tundra.
Investigators determined that the Caravan’s vertical and horizontal stabilizers had separated from the airplane after strik-ing the 207’s wing.
Engines Starved for Fuel
Cessna 421B. Substantial damage. No injuries.
About 10 minutes after departing from Fairhope, Alabama, U.S., for a VFR flight to Selma the afternoon of Sept. 29, 2012, the pilot repositioned the fuel selectors for both engines from the main tanks to the auxiliary tanks. He told investigators that later, when he initiated a descent from 4,500 ft, the right engine started to “cough and lose power.”
The pilot said that he repositioned the fuel selector to the main tank, but the engine lost power completely. He was unable to restart the engine. “The pilot did not select the [auxiliary] fuel boost pump to ‘low’ per the checklist, and as a result the sys-tem may have provided too much fuel to the engine for a restart,” the NTSB report said.
About two minutes after feathering the propeller on the right engine, the left engine began to lose power. “The airplane continued under partial power on the left engine for about six minutes, when the pilot realized that the airplane had descend-ed down to 800 feet,” the report said.
The pilot decided to land the airplane on a dirt road about 6 nm (11 km) from the Selma airport. After touchdown, the 421 crossed a bridge, clipped a tree and came to a stop in a cotton field with substantial damage to the right wing. The pilot and his three passengers escaped injury.
NTSB concluded that the probable cause of the accident was “the pilot’s improper fuel management, which resulted in a total loss of engine power on the right engine and a partial loss of engine power on the left engine due to fuel starva-tion.”
Brake Fails on Landing
Piper PA-31P. Substantial damage. No injuries.
The pilot said that shortly after the Pressurized Navajo touched down on the runway at Doylestown (Pennsylvania, U.S.) Airport the morning of Sept. 8, 2013, the left brake pedal “went to the floor.”
“He tried pumping the brakes to regain left braking action but was unsuccessful,” the NTSB report said. The landing gear collapsed when the Navajo veered off the runway and came to a stop in a grassy area. The pilot, alone in the air-plane, was not hurt.
“Post-accident examination confirmed that the left brake was inoperative and revealed a small hydraulic fluid leak at the shaft of the parking brake valve in the pressurized section of the cabin,” the report said. “Air likely entered the brake line at the area of the leak while the cabin was pressurized, rendering the left brake inoperative.”
‘Classic VMC Stall’
Piper Aztec. Destroyed. One serious injury.
The Aztec was about 100 ft off the ground on takeoff from Truckee-Tahoe (California, U.S.) Airport the morning of Sept. 21, 2011, when the left engine lost power. The pilot told investigators that the airplane rolled left and entered a “classic VMC stall.” (VMC is defined as the minimum control speed with the critical engine inoperative.)
The Aztec descended onto an airport parking ramp and was destroyed by fire. The pilot sustained serious injuries.
Investigators found that particles of paint clogging a fuel nozzle likely caused the engine problem. “However, even though the left engine may have been running rough and not producing full takeoff power, the right engine was oper-ating properly, and if the pilot had maintained airspeed at or above the airplane’s minimum controllable airspeed, he should have been able to maintain control,” the report said.
Bell 407. Substantial damage. One fatality.
The pilot was engaged in transporting passengers across a lake near Abingdon, Virginia, U.S., on Aug. 24, 2012. Night had fallen when a boater saw the helicopter deplane passengers and then lift off, turn toward the lake and descend along an embankment. The witness said that the landing light was not on when the skids subsequently contacted the water and the helicopter flipped over.
“Security camera video footage revealed that the pilot had successfully conducted this low-level, rapid-acceleration takeoff profile several times during the day, when visual spatial references were plentiful,” the NTSB report said. “The pi-lot’s decision to attempt such a takeoff at night without the aid of ambient light or the use of helicopter lights denied him the visual spatial references needed to assure safe terrain and obstacle avoidance.”
The report said that the pilot likely experienced a type of spatial disorientation called somatogravic illusion, in which acceleration is perceived as an increasing nose-up pitch attitude and can result in nose-down pitch inputs.
Rotor Blade Separates
Aerospatiale AS355 F1. Substantial damage. One fatality.
The helicopter struck terrain in West Windsor, New Jersey, U.S., after a main rotor blade separated during a positioning flight the afternoon of Sept. 15, 2012. Investigators found that the upper rod end on the fore/aft servo had disconnected due to severely worn threads in its fitting.
The NTSB report said that the helicopter operator’s “incorrect maintenance procedures and inadequate inspections” were contributing factors in the accident. Among the maintenance discrepancies was the use of a corrosion-inhibiting compound, rather than the grease specified in the maintenance manual, and an incorrect torque value during installation of the upper rod ends in the servos.
In addition, the inspection procedures provided by the helicopter manufacturer were found to be insufficient. “The 600-hour inspection called for checking the radial play of the end bearings,” the report said. “However, there were no instructions to spe-cifically check the threads of the servo end fitting or the torque of the rod end nut.”
Crash During Bird Avoidance
Bell 206L-3. Substantial damage. Two minor injuries.
The LongRanger was engaged in a public use flight to check a radiological monitoring system the afternoon of Sept. 7, 2013. The helicopter was in cruise flight about 300 ft above ground level near Amistad, New Mexico, U.S., when the pilot saw several large birds ahead.
The pilot initiated a steep right turn to avoid the birds. “He subsequently noted an increase in main rotor speed and ad-justed accordingly,” the NTSB report said. “The pilot rolled out on a reciprocal heading, leveled the helicopter and began to slow down. He noticed that the descent rate was not decreasing even though appropriate control inputs had been made.”
The helicopter touched down hard, bounced and came to a stop about 300 ft (91 m) from the touchdown point.