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.
Pitot Blocked by Ice
Boeing 757-200. Substantial damage. Seventeen minor injuries.
Inbound from Newark, New Jersey, U.S., with 131 passengers and eight crewmembers the morning of Oct. 20, 2013, the flight crew saw only light precipitation on their weather radar as they neared their destination in Dublin, Ireland.
Investigators later determined, however, that the on-board weather radar likely was not adjusted correctly and did not display an area of heavy precipitation that the 757 would encounter during the descent to Dublin.
The aircraft was about 80 nm (148 km) from Dublin, descending through 25,000 ft in instrument meteorological conditions, when it encountered turbulence that the copilot, the pilot flying, described as severe, said the report by the Air Accident Investigation Unit of Ireland.
The pilots also saw St. Elmo’s fire form on the aircraft. This phenomenon was described by the report as “a visible electrical discharge when an aircraft is flown through a heavily electrostatically charged atmosphere. It is often associated with nearby cumulonimbus or thunderstorm activity and/or flight through ice crystal.”
As the turbulence subsided, the copilot saw that the airspeed shown on his primary flight display (PFD) had dropped to about 90 kt. The report said that he likely was startled by this indication.
“The copilot, believing that the aircraft was about to stall, immediately pushed the control column forward and applied full power without disengaging the autopilot or autothrottle” in accordance with prescribed procedure, the report said.
“If the copilot had carried out the first actions of the aircraft manufacturer’s stall recovery checklist, which are to hold the control column firmly and disconnect the autopilot and autothrottle, it is likely he would have sensed the control loads on the control column, especially as he applied forward pressure. The control loads and pitch rate become more pronounced as the [airspeed] of the aircraft increases.”
Because he did not follow the procedure, the copilot did not sense the normal control loads. However, seeing the indicated airspeed increase in the dive, he began to raise the nose and reduce power. The indicated airspeed again began to decrease to a low value. Reacting to this indication and to the sound of the overspeed warning, which he misinterpreted as a stall warning, the copilot pushed the control column forward a second time.
The 757’s actual airspeed reached 380 kt — about 30 kt higher than the maximum operating speed. The report said that neither pilot noticed a master caution light or an “IAS [indicated airspeed] DISAGREE” annunciation, which was triggered by ice crystals that were blocking the pitot tube connected to the copilot’s air data computer.
The temporary blockage of the pitot tube caused the airspeed indications on the copilot’s PFD to be about 100 kt lower than those on the commander’s PFD and on the standby airspeed indicator.
“Following the second pitch-down manoeuvre, the flight crew concluded that the copilot’s airspeed indications were reading incorrectly and that the commander’s airspeed indications, which agreed with the standby airspeed indications, were correct,” the report said. “Consequently, the commander took control of the aircraft and returned it to stabilised flight.”
The cabin crew notified the pilots that a number of passengers (later determined as 13) and four flight attendants had sustained minor injuries from striking portions of the cabin. The report said that the injuries likely were caused by the rapid changes in positive and negative G-load during the “stall-recovery” maneuvers.
“The commander advised [Dublin approach control] that they had encountered severe turbulence and that medical assistance was required on arrival because some passengers had been injured,” the report said. He also requested that airport fire services attend the landing due to an indicated loss of the center hydraulic system.
The pilots landed the aircraft without further incident. Examination of the 757 revealed that the panel covering the center hydraulic system service bay had detached and had damaged system components, including the dump valve, leading to the loss of hydraulic fluid and pressure.
Brake Slows Takeoff Roll
Cessna Citation 550. Substantial damage. No injuries.
The flight crew detected nothing abnormal while preparing to depart from Lismore, New South Wales, Australia, the morning of Sept. 25, 2015. However, when the captain attempted to rotate the aircraft at the appropriate airspeed, 108 kt, the Citation did not achieve a sufficient takeoff pitch attitude.
“The captain then applied full back-pressure and reported that the controls felt very heavy,” said the report by the Australian Transport Safety Bureau (ATSB). “Neither the captain nor the copilot detected any change in the aircraft’s pitch attitude or any indication of pitch-up on the attitude direction indicator.”
The captain applied full braking and reverse thrust to reject the takeoff, but the Citation overran the 1,647-m (5,404-ft) runway. The nose landing gear collapsed, and the aircraft came to a stop on the wet, grass runway end safety area. Neither pilot was hurt.
Investigators determined that the Citation’s parking brake had not been released before takeoff. The resulting friction slowed acceleration during the takeoff roll but was not sufficient to prevent the aircraft from reaching rotation speed.
“Furthermore, the nose-down moment generated by the partial brake pressure probably prevented the aircraft [from] rotating sufficiently to become airborne, despite normal nose-up elevator deflection,” the report said. “Heat in the brakes due to partial pressure during the takeoff run may have reduced their effectiveness when the captain rejected the takeoff, contributing to the runway overrun.”
The ATSB recommended that the manufacturer take action to address the absence of an annunciator showing that the parking brake is engaged and the absence of a parking brake check on the Citation 550’s “Before Takeoff” checklist.
‘Limited Runway Remaining’
Airbus A319. No damage. No injuries.
Before boarding the A319 for a flight from Lisbon, Portugal, to Basel, Switzerland, the afternoon of Oct. 16, 2015, the flight crew discussed the weather conditions, which included light and variable surface winds, and the possibility that they would depart from Runway 03.
Although the automatic terminal information service indicated that Runway 21 was in use, the crew subsequently used their electronic flight bag to derive performance data for a departure from an intersection of Runway 03, which would provide a takeoff distance of 3,530 m (11,582 ft). The data then was entered into the aircraft’s flight management guidance computer.
“During this time, the commander’s attention was distracted by people entering the cockpit,” said the report by the U.K. Air Accidents Investigation Branch.
Neither pilot later noticed the data discrepancy when they were cleared for takeoff from an intersection of Runway 21, which provided a takeoff distance of 2,410 m (7,907 ft).
“The crew considered the takeoff normal until the aircraft approached V1, when they noticed there was limited runway remaining, but the remainder of the flight was uneventful,” the report said. (V1 is defined as the maximum speed during takeoff at which the pilots must take the first action to stop the airplane within the accelerate-stop distance.)
The aircraft, with 147 passengers and six crewmembers aboard, had lifted off with 213 m (699 ft) of runway remaining.
“The commander later commented that this occurrence was a result of multiple distractions during pre-flight preparation and some complacency as a result of operating from his home base,” the report said.
“The commander added that in the future, if he is interrupted during a brief or crosscheck of data, he will start the process again to ensure that it is completed fully.”
Control Lost at Night
Fairchild Metro 3. Destroyed. Two fatalities.
Night visual meteorological conditions (VMC) prevailed for the cargo flight from the Dominican Republic to San Juan, Puerto Rico, on Dec. 2, 2013. Nearing the destination, the flight crew was cleared by air traffic control (ATC) to descend from 11,000 ft to 3,000 ft.
“During the descent, at about 7,300 ft and 290 kt, the airplane entered a shallow left turn, followed by a 45-degree right turn and a rapid, uncontrolled descent, during which the airplane broke up about 1,500 ft over uneven terrain,” said the report by the U.S. National Transportation Safety Board (NTSB).
Investigators concluded that the flight crew had lost control of the Metro, but they were unable to determine why. The airplane, which had no data recorders or downloadable avionics memory, had been loaded properly, and there was no sign of an initiating mechanical failure or abnormality.
“Other similarly documented accidents and incidents generally involved unequal fuel burns, which resulted in wing drops or airplane rolls,” the report said. “However, [the Metro’s] fuel crossfeed valve was found in the closed position, indicating that a fuel imbalance was likely not a concern of the flight crew.”
The report said it was likely that the breakup was precipitated by overstress during attempted recovery from the control loss.
“With darkness and the rapid descent at a relatively low altitude, one or both crewmembers likely pulled hard on the yoke to arrest the downward trajectory and, in doing so, placed the wings broadside against the force of the relative wind, which resulted in both wings failing upward,” the report said.
“As the wings failed, the propellers simultaneously chopped through the fuselage behind the cockpit. At the same time, the horizontal stabilizers were also positioned broadside against the relative wind, and they also failed upward.”
Glass Beads Cause Engine Failure
Cessna 208. Substantial damage. No injuries.
The Caravan was climbing through 8,000 ft after departing from Kahului, Hawaii, U.S., for a charter flight the evening of Oct. 21, 2013, when the flight crew heard a loud bang and a grinding sound, and saw sparks emerge from the engine’s right exhaust pipe.
The engine lost power, and the crew turned back toward Kahului Airport, 13 nm (24 km) north. “The crew accomplished the emergency checklists and elected to perform an emergency landing on a highway,” the NTSB report said.
“During the landing roll, the airplane struck two highway traffic signs, which resulted in substantial damage to the right wing.” The pilots and their eight passengers were not injured.
Examination of the engine revealed that all of the blades on the compressor disc had separated, and glass beads and bead fragments were found embedded in the blade “fir-tree” attachment joints.
This indicated that the compressor disc, fully assembled, had been cleaned by aggressive bead-blasting, likely when the engine was removed for repair about two months before the accident, the report said.
“The engine manufacturer specifies that all media-blast cleaning be performed with the [compressor] disc and blades disassembled,” the report said. “The glass bead contamination of the fir-tree joints caused the [compressor] blades to be unevenly restrained, and it altered the blades’ designed vibration frequency, making them susceptible to the aerodynamic vibrations from the combuster gas flow.
“Therefore, the fatigue fracture of the blades was most likely due to the glass bead contamination.”
Tire Bursts on Takeoff
Bombardier Q400. Substantial damage. Three minor injuries.
The inboard tire on the right main landing gear ruptured as the aircraft reached rotation speed on takeoff from Calgary, Alberta, Canada, the night of Nov. 6, 2014. The flight was scheduled to land at Grand Prairie, but the flight crew decided to divert to Edmonton.
During the approach to Edmonton, the pilots received indications that the landing gear was down and locked. However, the right main landing gear collapsed shortly after touchdown.
“Upon contact with the ground, all of the right-side propeller blades were sheared, and one blade penetrated the cabin wall,” said the report by the Transportation Safety Board of Canada (TSB). Three passengers were injured by debris from the propeller impact.
The Q400 came to a stop off the right edge of the runway, and the passengers and crew evacuated using all four exits. There were no injuries during the evacuation.
The TSB concluded that the tire rupture on takeoff from Calgary “most likely [was the] result of impact with a hard object.”
Water in Fuel System
Britten-Norman Islander. Destroyed. Three fatalities, one serious injury.
The airport at St. John’s, Antigua, had been closed due to thunderstorms and heavy rain, and was reopened shortly before the Islander was cleared to depart on a visual flight rules (VFR) scheduled flight to Montserrat the morning of Oct. 7, 2012.
The pilot did not drain the fuel system sumps during preflight preparations or conduct power checks before initiating a takeoff to the northeast, toward the sea, from a runway intersection, said the report by the Eastern Caribbean Civil Aviation Authority.
Witnesses saw the Islander climb about 200 to 300 ft, roll right and descend to the ground near the runway departure threshold. Two passengers and the pilot were killed, and another passenger was seriously injured.
Investigators determined that the right engine had lost power due to contamination of the fuel supply by water. The fuel filler caps on the airplane were of a type included in an equipment modification designed to prevent water from entering the fuel system. However, the adaptor plates were original equipment and had not been replaced in conformance with the modification.
“Although the caps appeared to fit satisfactorily, it was found that the right tank cap did not always seal properly, with corrosion on the adaptor plate possibly contributing to this condition,” the report said. “A simple experiment indicated that water could leak past the cap seal and into the tank.”
The report said that the right fuel tank contained a significant amount of water that could have been detected if the pilot had checked the sumps before takeoff.
Beech 58 Baron. Destroyed. Three fatalities.
Marginal VMC, including 6 mi (10 km) visibility, a broken ceiling at 1,000 ft and an overcast at 1,700 ft, prevailed when the Baron departed from Midway Airport in Chicago for a VFR flight to Kansas the night of Oct. 12, 2014.
Recorded ATC radar data indicated that the Baron entered the clouds shortly after takeoff. Track and altitude then varied substantially before the airplane entered a descent exceeding 5,000 fpm and struck the ground. The pilot and his two passengers were killed.
The pilot was certified for instrument flight in multiengine airplanes but had not filed a flight plan. “The airplane’s avionics and instruments could not be functionally tested due to the extent of the impact damage,” the NTSB report said.
The NTSB concluded that the probable cause of the accident was “the pilot’s loss of airplane control due to spatial disorientation while operating in night instrument meteorological conditions.”
Too Late to Go Around
Piper Twin Comanche. Substantial damage. No injuries.
A 15-kt crosswind existed at the airstrip in Innamincka Township, South Australia, where a fly-in was being held on Oct. 26, 2012. “As a precaution, the pilot elected to increase the aircraft’s airspeed for the approach by about 5 kts and selected 1/2 flaps,” the ATSB report said.
The Twin Comanche was high on the approach and was flared for landing about 100 ft above the 980-m (3,215-ft) gravel runway. “The aircraft floated and touched down about a quarter [of] the way along the runway,” the report said. The pilot reduced power to idle and applied light wheel braking.
The aircraft was about halfway down the runway when the pilot realized that groundspeed was excessive. “The pilot determined that it was too late to commence a go-around” and applied full braking, the report said. “He reported that the braking appeared to be ineffective due to the surface of the runway, and the aircraft continued beyond the runway end.”
Damage was substantial, but the pilot and his passenger were not hurt.
Bell 206B-3. Substantial damage. One serious injury, two minor injuries.
The pilot made several practice approaches and landings before beginning flights to transport passengers to a rock ledge on Mount Cook in Queensland, Australia, on the morning of Oct. 7, 2014.
During the practice landings, he decided that resting the right skid on the edge of the ledge was preferable to touching down on the uneven surface with both skids.
After transporting five passengers to the ledge, the pilot returned to pick up some of the passengers. The JetRanger was lifted by a gust of wind on touchdown, and the right skid began to scrape along the surface of the ledge. The helicopter then rolled onto its right side, slid and struck two waiting passengers.
One passenger was seriously injured; the other passenger and the pilot sustained minor injuries.
“The roll onto the right side by the helicopter is consistent with the phenomenon known as dynamic rollover,” the ATSB report said. “When a helicopter rests on one skid, the aircraft may begin rolling, and under certain circumstances it cannot be controlled.”
‘Low Risk, Go Flying’
Airbus AS350. Substantial damage. No injuries.
Before departing to pick up four seismic workers near Deadhorse, Alaska, U.S., the afternoon of Oct. 26, 2015, the pilot conducted a risk assessment of the landing site, where visibility was between 1 and 3 mi (1,610 m and 4,831 m).
“The assessment fell within the ‘low risk, go flying’ category, and a VFR company flight plan was filed,” the NTSB report said.
The pilot, who was not certified for instrument flight, encountered deteriorating weather en route and flat-light conditions at the landing site. “While slowing down to land, blowing snow from the main rotor downwash subsequently reduced the visibility to whiteout conditions with no ground reference, which likely led the pilot to experience spatial disorientation,” the report said.
The right skid snagged the ground on touchdown, and the helicopter rolled onto its side. Damage was substantial, but the pilot was not hurt.
Preliminary Reports, July 2016 [PDF 50K]