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.
Stick Shaker Activated
Boeing 737-800. No damage. No injuries.
The 737 was en route with 140 passengers and six crewmembers the evening of Jan. 7, 2012, from East Midlands Airport in England, to Riga Airport in Latvia, where weather conditions were deteriorating. As the aircraft neared the airport, Riga was reporting a 500-ft overcast and a runway visual range of 1,800 ft (550 m) in rain and snow.
Shortly after entering a cloud layer at 6,000 ft during descent, the flight crew noticed a discrepancy in their primary flight display (PFD) indications. The first officer, the pilot flying, saw indications that airspeed was decreasing and that the descent rate was increasing, while the commander saw an indication that airspeed had increased to about 280 kt.
The first officer disengaged the autopilot and autothrottle system, and leveled the aircraft at 4,000 ft. “When the flight crew cross-checked, they noticed ‘IAS DISAGREE’ [and ‘ALT DISAGREE’] warnings on the PFDs and that the first officer’s altimeter read 250 ft higher than the commander’s,” said the report by the Air Accident Investigation Unit of Ireland (AAIU).
While conducting the quick reference handbook (QRH) “IAS Disagree” checklist, the pilots confirmed that pitot heat was selected on and that there were no indications of a pitot heat failure. A cross-check of the standby flight instruments and the inertial reference system showed that the commander’s instruments were providing correct indications.
The commander then took control, and the crew resumed the approach. “Air traffic control volunteered and helpfully gave groundspeed readouts,” the report said.
Shortly after the flaps were extended, the first officer’s stick shaker (stall-warning system) activated. “As the stick shaker continued until the aircraft had landed, the crew commented that they found this very distracting, and the noise made communications difficult,” the report said. “Although … the circuit breaker for the stick shaker could have been pulled, they felt that it was unwise to look for [it] in a dark cockpit and in the prevailing circumstances.”
The crew re-engaged the autopilot and autothrottles, but both systems soon disengaged automatically. The commander continued the approach manually, and after sighting the runway at 300 ft, the crew landed the 737 without further incident.
The report said that a short circuit had developed in the heating element in the pitot probe on the first officer’s side, but the circuit had remained open. Because electrical power continued to be supplied to the heater, no warning of its failure was provided. The consequent ice build-up on the probe caused the air-data discrepancies.
The report noted that 20 similar incidents had been reported by the aircraft operator. “In the majority of the cases reported, the airspeed divergences returned to normal as the probe ice melted during the descent into the warmer temperatures at lower altitudes,” the report said.
Based on these findings, the AAIU recommended that the U.S. Federal Aviation Administration and Boeing review the pitot heating systems in 737NG series aircraft and provide guidance in the QRH about other systems that can be affected and about warnings that can be generated as a consequence of pitot system failure.
Deicing Fluids Smoke Cabin
Airbus A319-111. No damage. One minor injury.
The airport traffic controller had asked the flight crew to keep their speed up while vacating the runway after landing, and reverse thrust was still being used when the A319 was turned onto a taxiway at Belfast (Northern Ireland) International Airport the night of Jan. 6, 2011.
“Smoke began to enter the cabin, and the cabin manager advised the flight crew,” said the report by the U.K. Air Accidents Investigation Branch. “As the smoke became thicker, the cabin manager recommended that an evacuation was necessary.”
Passengers and crewmembers later described the smoke as being brown or black in color, with an odor of a bonfire or an electrical fire, the report said.
The commander stopped the aircraft on the taxiway and shut down the engines; the cabin crew initiated an evacuation. One of the 46 passengers sustained minor injuries while vacating an evacuation slide.
Investigators found that the airport’s runways and taxiways had been treated with deicing chemicals (potassium acetate and urea) before the A319 was landed. “The deicing chemicals were most probably the source of the smoke, the density of which was probably exacerbated by the prolonged use of reverse thrust,” the report said. “It seems likely that the deicing chemicals were ingested into the engine before passing through the air conditioning system and entering the cabin through the overhead vents.”
‘Hold Position’ Misunderstood
Boeing 767-300. No damage. No injuries.
The flight crew of the 767, registered in the United States as N588HA, was told by an air traffic controller to hold short for departure from Runway 06R at Kansai International Airport in Osaka, Japan, the night of Oct. 12, 2011. Three aircraft, including a 767 registered in Japan as JA8356, were on approach to the runway.
“When an arriving aircraft passed in front of N588HA that had been holding, the air traffic controller instructed N588HA again to hold and then cleared JA8356 to land,” said the report by the Japan Transport Safety Board (JTSB).
Nevertheless, the controller then saw N588HA begin to taxi onto the runway, and he instructed the crew of JA8356 to go around. The 767 was about 4 nm (7 km) from the runway when the go-around was initiated. None of the 208 people aboard N588HA or the two pilots of JA8356 were injured.
The JTSB concluded that the probable cause of the runway incursion was the U.S. crew’s misunderstanding of the controller’s instruction to continue holding, which was phrased similarly to an instruction previously used in the United States to tell flight crews to hold on the runway for takeoff (i.e., “taxi into position and hold”).
The controller’s initial instruction was to “hold short of runway zero six right.” However, the controller later repeated the instruction by saying “hold position, expect departure after next arrival five miles.” The flight crew read back the instruction as “position hold.”
“The controller did not know that the phraseology used in the readback was previously used in the U.S. to instruct aircraft to hold on the runway,” the report said. (The current phraseology, which conforms to International Civil Aviation Organization standards, is “line up and wait.”)
Elevator Controls Freeze
Cessna Citation 560XL. No damage. No injuries.
The Citation was en route with two passengers from Fort Pierce, Florida, U.S., to Atlanta, Georgia, the night of Jan. 13, 2013. As it climbed in instrument meteorological conditions (IMC) through 35,000 ft to the assigned Flight Level (FL) 380 (approximately 38,000 ft), the airplane pitched nose-down and entered a 400-fpm descent.
The flight crew disengaged the autopilot and leveled off at FL 350. “Both crewmembers noted that ‘excessive’ force was required to change the pitch of the airplane and notified air traffic controllers of the situation,” said the report by the U.S. National Transportation Safety Board (NTSB). The crew requested and received clearance to descend.
The pilots later told investigators that as the Citation descended through 18,000 ft, something “broke loose” and the elevator controls began to respond normally again. The crew subsequently completed the flight without further event.
Examination of the airplane revealed that several of the fuselage bilge drain holes were partially or totally obstructed by debris, allowing water to accumulate in the bilge. Investigators also found that tail cone seals had been installed improperly.
The NTSB concluded that water likely had entered the tail cone through the improperly installed seals and had frozen around elevator-control components, causing the flight control stiffness the crew experienced. “The ice subsequently melted as the airplane descended, and the pilots were able to regain control,” the report said.
Turbulence, Ice Cause Control Loss
Beech King Air E90. Destroyed. Two fatalities.
Widely scattered thunderstorms prevailed along the pilot’s intended route from Amarillo, Texas, U.S., southeast to Fort Worth the afternoon of Dec. 14, 2012. Shortly after takeoff, an air traffic controller cleared the pilot to climb to FL 210 and approved his request to deviate east of course to avoid weather.
The King Air was climbing through 14,800 ft when it unexpectedly turned north. “The controller queried the pilot about the turn; however, he did not respond,” the NTSB report said. Recorded radar data showed that the airplane then entered a steep descent.
The wreckage was found on ranch land near Amarillo. The outer wing sections, engines and tail control surfaces had separated, indications of an in-flight break-up.
“Post-accident airplane examination did not reveal any mechanical malfunctions or anomalies with the airframe or engines that would have precluded normal operation,” the report said. “It is likely the airplane encountered heavy to extreme turbulence and icing conditions during the flight, which led to the pilot’s loss of control of the airplane.”
Glideslope Signal Disrupted
ATR 72-200. No damage. No injuries.
The aircraft was on a scheduled flight the morning of Dec. 19, 2011, with 13 passengers and four crewmembers from Dublin, Ireland, to Kerry, which had unrestricted visibility and a broken ceiling at 500 ft.
The flight crew later told investigators that, while conducting the instrument landing system (ILS) approach to Runway 26, the autopilot “chased” (deviated slightly above and below) the glideslope and then, about 9 nm (17 km) from the runway, pitched the aircraft nose-down.
The ATR was in a 2,000-fpm descent and the enhanced ground-proximity warning system was generating terrain warnings when the crew disengaged the autopilot and conducted a go-around.
Similar problems were encountered during the second ILS approach, so the crew again disengaged the autopilot and reverted to a hand-flown localizer approach, which was completed without further incident.
“Subsequent examination by the operator found that the unstable reception of the ILS glideslope signal was caused by a missing reflective strip from inside the aircraft’s radome, which had been recently repaired,” the report said. “The metallic strip, a ‘glideslope antenna deflector,’ … is used to concentrate the glideslope beam towards the glideslope antenna. The ILS [equipment] on the aircraft is considered unserviceable if the strip is missing.”
Standing Water on Runway
Fairchild SA226-TC. No damage. No injuries.
En route from Thangool, Queensland, Australia, on a charter flight with 11 passengers to Archerfield the afternoon of Jan. 23, 2014, the pilot received the automatic terminal information service broadcast, which said that there were a few clouds at 800 ft, a broken ceiling at 1,900 ft and that the runway was “wet.”
The pilot conducted the nondirectional beacon (NDB) approach and circled to land on Runway 10L. However, he subsequently initiated a go-around because the Metroliner was not aligned properly with the runway, said the report by the Australian Transport Safety Bureau (ATSB).
Heavy rain was falling when the pilot conducted another NDB approach and landed the aircraft on Runway 10L. “The pilot reported that as the wheels touched down, the aircraft commenced sliding towards the right, possibly due to aquaplaning,” the report said. He reduced the power levers to the ground idle setting. The aircraft veered off the right side of the runway and onto the grass.”
An inspection of the runway revealed that it was contaminated with standing water up to 50 mm (2 in) deep. The report noted that Airservices Australia defines a “wet” runway as one with a “surface [that] is soaked but there is no standing water.” The term water patches is used to indicate that “patches of standing water are visible.”
“The oversight of runway condition [at Archerfield Airport] was difficult from the [control] tower perspective, as the runway was up on a rise and appeared as just a thin slither of bitumen,” the report said. “Any pooling or extensive standing water was not easily visible from the tower cab.”
Although the airport operations and technical officer conducted a visual inspection of the runway each morning, further visual inspections were conducted only on request by an aircraft operator or a tower controller.
Fuel Selectors on Empty Tanks
Piper Navajo. Substantial damage. No injuries.
Before departing from Aldinga, South Australia, the morning of Jan. 29, 2012, the pilot checked the main and auxiliary fuel tanks but inadvertently left the fuel selectors positioned to the auxiliary tanks, which were nearly empty. He had the main tanks refueled before starting the engines.
The pilot conducted the pre-takeoff checklist from memory “but did not complete his usual final check, which was to reach down with his right hand and confirm that the fuel selector levers were on the main tanks,” the ATSB report said.
The fuel selectors were still on the auxiliary tanks when the pilot began the takeoff. “Almost immediately [after rotation] both engines began surging, there was a loss of power, the power gauges fluctuated and the aircraft yawed from side to side,” the report said. The pilot landed the airplane straight ahead on an open field.
The ATSB concluded that the forced landing likely was caused by inadequate preflight preparation and fuel starvation.
“The pilot stated that the large mental workload of running a business may have taken some of his attention from an intended routine flight to a known destination on a clear day,” the report said. “This most likely contributed to his not reselecting the main tanks prior to start-up and also not completing his usual memory checks … during the pre-takeoff checks.”
Ice, Tail Wind Factor in Overrun
Beech Queen Air. Substantial damage. No injuries.
The pilot was on a cargo flight the morning of Jan. 11, 2013, from Minneapolis, Minnesota, U.S., to Alexandria, which had 1 mi (1,600 m) visibility, a 200-ft overcast and surface winds from 180 degrees at 7 kt. He decided to conduct the ILS approach to Runway 31.
The NTSB report noted that the pilot did not request or receive information on the condition of the 5,100-ft (1,554-m) runway, which was contaminated with ice at the time.
At decision height, the pilot saw the visual approach slope indicator and runway end identifier lights, and continued the approach. He later told investigators that the brakes alternately “skidded and grabbed” after the Queen Air touched down about 1,000 ft (305 m) past the threshold.
“The pilot decided not to go around and to remain on the runway and attempt to stop the airplane,” the report said. The Queen Air overran the runway onto snow-covered terrain. The left wing spar was substantially damaged when it struck an ILS antenna pylon.
Visual Flight in Fog and Rain
Piper Cherokee Six. Substantial damage. Two fatalities.
Night IMC prevailed when the pilot departed under visual flight rules from St. Ignace, Michigan, U.S., the morning of Dec. 3, 2011, for a charter flight to Mackinac Island, which is about 5 nm (9 km) southeast in Lake Huron.
As the single-engine airplane neared the airport, the Mackinac automated weather observing system was reporting 7 mi (11 km) visibility, a broken ceiling at 300 ft and a 700-ft overcast. Residents near both airports reported fog and rain in the area.
“The pilot did not land on the island but was returning to the departure airport with the passenger still on board when the airplane contacted trees and terrain about 1.4 miles [2.3 km] north of the airport,” the NTSB report said. “No pre-accident mechanical failures or malfunctions with the airplane were identified that would have precluded normal operation.”
The NTSB concluded that the probable causes of the accident were “the pilot’s decision to initiate visual flight in instrument meteorological conditions and subsequent failure to maintain adequate altitude.”
Intoxicated Pilot Loses Control
Robinson R44. Destroyed. One fatality.
During one of several stops at oil-production facilities near Fox Creek, Alberta, Canada, on Jan. 27, 2013, “the pilot was observed to be staggering and smelling of alcohol,” said the report by the Transportation Safety Board of Canada (TSB). “On being questioned, the pilot uttered some derogatory remarks.”
The pilot later disembarked a passenger at a company facility. “The helicopter was observed to be flying erratically during departure,” the report said. “It broke up in flight over a wooded area five minutes later.”
Examination of the wreckage showed that one main rotor blade had failed in overload and had separated from the helicopter; the other rotor blade had struck the cabin.
Noting that toxicological tests of the pilot revealed high levels of ethanol, the TSB concluded that “while piloting the helicopter under the influence of alcohol, the pilot made flight control inputs that caused the main rotor blade to contact the cabin and precipitate the in-flight breakup.”
Spatial Disorientation on Dark Night
Bell 206B-3. Destroyed. One fatality.
The pilot discontinued a crop frost-protection flight at about 0600 local time on Jan. 2, 2013, when fog began to accumulate over the field. She was returning to her base in Delano, California, U.S., when the JetRanger struck terrain about 10 nm (19 km) from the airport.
Investigators determined that the helicopter was in a steep right turn upon impact. No indication of a pre-impact mechanical malfunction or failure was found. The NTSB concluded that the pilot had become spatially disoriented.
“The dark night conditions, sparsely lit terrain and accumulating fog reduced the visual cues available for the pilot to maintain orientation, and, under those conditions, the helicopter’s external spotlights … could have further reduced or provided misleading visual cues,” the report said. “These conditions were conducive to the development of spatial disorientation.”
Chasing Some Birds
Robinson R44. Substantial damage. One serious injury, two minor injuries.
The pilot was flying the helicopter at 100 kt about 200 to 250 ft above Roosevelt Lake, Arizona, U.S., on Dec. 7, 2012. He later told investigators that the lake water was very clear and perfectly calm.
“The pilot [said that he] looked inside the cockpit to check instruments, and when he looked outside and below the helicopter, he experienced a feeling of mental confusion similar to vertigo,” the NTSB report said. “At this point, the pilot estimated that the helicopter was between 15 and 20 ft above the water. He pulled aft on the cyclic; the helicopter impacted the water, pitched forward and sank.
“One of the passengers stated that moments before the collision with the water, the pilot had asked them if they wanted to get closer to the water [and] chase some birds.”