Inadvertent Descent Below Minimums

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.

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Jets

TCAS WaRnings Dismissed

Boeing 737-300. No damage. No injuries.

Several factors increased the risk involved in the airline’s addition of a new stop on its scheduled passenger service. Among the risk factors at the new stop at Kosrae International Airport in the Federated States of Micronesia were high terrain, absence of a control tower and the availability of only nonprecision approach procedures.

Moreover, there was only one procedure that the flight crew could conduct: a circling nondirectional beacon/distance measuring equipment (NDB/DME) approach. The 737 was not suitably equipped for either of the two global positioning system (GPS) approaches at the airport, and the airline was not authorized to conduct GPS approaches.

The captain had flown to Kosrae only twice before, and in day visual meteorological conditions (VMC). On the day of the inaugural flight — June 12, 2015 — instrument meteorological conditions (IMC) prevailed at the airport.

In addition, the captain was experiencing fatigue. Due to the illness of a family member, he had received less than six hours of sleep the night before the flight and had been awake for about 13 hours on arrival at Kosrae.

The risks had mounted as the flight progressed. Weather conditions at the airport were deteriorating rapidly, and delays experienced during two previous stops meant that the aircraft would reach the airport after nightfall. As the risks mounted, the stress on the flight crew built to a degree that it affected their decision making and performance, according to the Australian Transport Safety Bureau (ATSB).

Nearing Kosrae, the crew found that surface visibility had decreased to 3 mi (4,800 m), the published minimum visibility for the NDB/DME approach. The pilots decided that they would attempt one approach and, if unable to land, they would attempt only one more approach before diverting to their alternate airport.

During the approach briefing, the captain mentioned what he perceived as an unusually low transition altitude at Kosrae. The transition altitude — at which they were supposed to reset their altimeters from the standard 29.92 in Hg to the local barometric pressure, 29.74 in Hg — was 5,500 ft at Kosrae. The captain told the first officer that the transition altitudes at the airports to which he usually flew were above 10,000 ft.

Despite this discussion, the crew did not remember to reset their altimeters at the transition altitude. They also did not complete the approach checklist, which included an altimeter setting check. The result was that the altitude shown on their altimeters was 180 ft above the altitude at which the aircraft actually was flying. Thus, when the crew descended to the minimum descent altitude for the approach (500 ft), the aircraft actually was at 320 ft (309 ft above the ground).

The enhanced ground-proximity warning system (EGPWS) generated three “too low, terrain” warnings, but the crew believed they were spurious warnings caused by an inertial reference system map shift anomaly. “The crew were not aware that the EGPWS had its own internal GPS [receiver],” the ATSB report said. The pilots also were unaware that they were below minimums for the nonprecision approach.

The 737 was in IMC when it reached the missed approach point, and the crew did not have visual contact with the runway. The captain initiated a missed approach by disengaging the autopilot and autothrottle. He manually increased the aircraft’s pitch attitude to about 15 degrees nose-up but did not properly select takeoff/go-around (TOGA) power. (He pressed the TOGA switch only once, which increased thrust to a value below maximum; two presses are required to select full go-around thrust, the report said.)

“The captain observed the airspeed decay and pitched the aircraft down to increase the airspeed,” the report said. “The first officer stated he called ‘sink rate’ twice. The captain then realised and rectified the situation, depressing the TOGA switch a second time, commanding full go-around thrust.” After completing the missed approach procedure, the crew conducted another NDB/DME approach and landed the 737 without further incident.

Collision With A Fuel Truck

Cessna Citation Mustang. Substantial damage. No injuries.

The Citation had been parked for more than 30 minutes after a previous flight when the pilots began preparations for a training flight at London Biggin Hill Airport the morning of June 15, 2017. The commander was a type-rating examiner, and the copilot was completing training for his type rating in the Cessna 510.

The aircraft had been refueled, and the fuel truck had been backed away. Although the commander believed that the truck was well clear of the Citation, the truck driver had stopped a short distance from the aircraft to allow other ground vehicles to pass by.

“Before the crew began their flight deck checks, the commander realised there were no ground personnel immediately available, so he went outside to remove the wheel chocks,” said the report by the U.K. Air Accidents Investigation Branch. “He stood to the left of the aircraft, which was parked on a slight slope, and signaled to the copilot to set the aircraft’s parking brake.”

The copilot depressed the brake pedals, engaged the parking brake handle and gave the captain a thumbs-up signal. The commander removed the wheel chocks and moved away to place the chocks on the ground clear of the Citation. “When he turned back, he saw the aircraft was rolling towards the fuel bowser and called to the copilot to apply the brake,” the report said. “He could see the copilot was trying to apply the brake, but the aircraft did not stop until it hit the fuel bowser.”

The leading edge of the left wing and the forward fuselage of the Citation were substantially damaged. The fuel truck also was damaged during the collision.

The flight crew were aware that an accumulator stores hydraulic pressure for the braking system. However, the pilot training manual for the Citation does not indicate how long the accumulator can maintain pressure after the electric hydraulic pump is disengaged.

“The copilot had no previous experience using a pressurized brake system and was not aware of a requirement to complete any checklists before attempting to set the parking brake,” the report said. The checklist requires in part that the battery switch be turned on to supply power to the electric hydraulic pump before engaging the parking brake.

“The commander was surprised to discover after the accident that it is not unusual for the hydraulic system pressure to dissipate within 30 minutes of electric power being disconnected,” the report said. “He had anticipated that there would be pressure available to actuate the brakes without turning on the battery.”

Fuel Leak Causes Engine Fire

Boeing 777-300ER. Substantial damage. No injuries.

The 777 was about two hours into a flight from Singapore to Milan, Italy, the morning of June 27, 2016, when the flight crew received an indication of low oil quantity in the right engine. Shortly thereafter, they felt a vibration through their control columns and decided to return to Singapore.

“Shortly after landing in Changi Airport, a fire was observed to have occurred in the vicinity of the aircraft’s right engine,” said the report by the Singapore Transport Safety Investigation Bureau. “After the aircraft came to a stop on the runway, a fire developed under the right wing.”

Airport rescue and fire fighting personnel extinguished the fire, and all 241 occupants of the 777 evacuated on mobile stairs. There were no injuries. Examination of the aircraft revealed substantial heat damage to the right engine core, portions of the cowlings and the wing.

Investigators determined that the fire had erupted when fuel leaking from a cracked engine fuel pipe was ignited on contact with an exhaust nozzle during deployment of thrust reversers after touchdown. “As the fire developed, it propagated towards the forward section of the engine and entered the core of the engine through the fan booster inlet,” the report said.

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Turboprops

Landing ‘at All Costs’

Saab 340B. Substantial damage. No injuries.

The aircraft was in VMC for most of the scheduled flight with 21 passengers and three crewmembers from Fort Lauderdale, Florida, U.S., to Marsh Harbor, Abaco, Bahamas, the afternoon of June 13, 2013. Nearing the destination, however, the flight crew saw that there was a thunderstorm moving over the airport. “The non-flying pilot (the captain) was adamant about landing at all costs,” said the report by the Air Accident Investigation Department of the Bahamas.

There were no instrument approaches and no control tower at the airport. The crew canceled their instrument flight rules flight plan and conducted a visual approach to Runway 09. “As the approach continued, there were constant disagreements between the pilots as to who had the runway in sight,” the report said. “Yet the crew continued descending visually in an attempt to land the aircraft on a runway that was not in sight.”

The Saab was less than 500 ft above the ground on final approach when the captain assumed control of the aircraft. His windshield wiper then failed, and the first officer assumed control. “Seconds before touchdown, the captain, despite having no visual contact with the runway due to the intense downpour of rain and the non-use of his windshield wiper, again took control of the aircraft from the first officer.”

The aircraft bounced three times after touchdown, with each bounce progressively higher. The Saab rose 27 ft during the last bounce, and the nose landing gear collapsed when the the aircraft hit the runway again. “It is possible the [right] wing may have started to fail at this point,” the report said. The aircraft veered off the right side of the runway and struck a drainage ditch before coming to a stop. Damage was substantial, but there were no reports of injuries.

“Complacency was the order of the day,” the report said. “The crew had several opportunities to either divert to an airport with visual weather or hold and wait for the thunderstorm over the field to pass. Instead, they elected to try and beat the weather.”

Oil Leak Causes Engine Fire

ATR 72-500. Substantial damage. Three minor injuries.

Shortly after departing from Bangalore, India, for a flight to Mangalore the morning of June 15, 2016, the flight crew noticed the master caution light illuminate briefly but saw no other sign of an anomaly. Moments later, they received a call from the lead cabin crewmember about light, white smoke in the cabin. The pilots completed the pertinent checklists, declared an urgency and turned back to Bangalore.

“The smoke kept on thickening, but the source of the smoke could not be identified,” said the report by the committee of inquiry appointed by India’s Ministry of Civil Aviation. “Passengers were given wet tissues and issued instructions to bend down.”

The captain told the cabin crew to prepare for an emergency evacuation on the runway. During the preparations, passengers reported seeing flames emerging from the right engine. At the same time, the flight crew received warnings of an engine fire. After completing the engine fire checklist and shutting down the right engine, the crew declared an emergency. The ATR was landed shortly thereafter at Bangalore. Three of the 67 passengers sustained minor injuries during the evacuation.

Investigators found that two second-stage power turbine blades had failed, one from fatigue and the other from overload. The subsequent vibration caused air/oil seals for the turbine shaft and impeller bearings to fail, allowing oil to enter the engine bleed-air system.

Headsets Cancel Gear Warning

Swearingen Metroliner. Substantial damage. No injuries.

The pilot-in-command (PIC) was conducting a training flight with a newly hired copilot the afternoon of June 20, 2016. During a visual approach to Farmingdale, New York, U.S., the pilots did not maintain a sterile cockpit and did not complete the Before Landing checklist, said the report by the U.S. National Transportation Safety Board (NTSB). As a result, the landing gear was not extended during the approach.

The copilot, the second-in-command (SIC), was flying the Metroliner from the left seat. “The PIC asserted that there was no indication that the landing gear was not extended because he did not hear a landing gear warning horn,” the report said. “He added that the landing gear position lights were not visible because the SIC’s knee obstructed his view of the lights.”

As the SIC flared for touchdown, the PIC heard the propellers strike the runway. “He made the decision not to go around because of unknown damage sustained to the propellers,” the report said. “The airplane touched down and slid to a stop on the runway.” Neither pilot was injured. Examination of the Metroliner revealed substantial damage to fuselage bulkheads, longerons and stringers.

Noting that both pilots were using noise-canceling headsets, the report said, “The landing gear warning horn was presented by an aural tone in the cockpit and was not configured to be heard through the pilots’ noise-cancelling headsets.”

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Piston Airplanes

Chasing the Glideslope

Piper Navajo. Destroyed. Two fatalities.

The pilot had conducted charter flights several times with the passenger from Washington, Pennsylvania, to University Park Airport in State College. On the morning of June 16, 2016, IMC prevailed along the route, and the destination airport was reporting 1 mi (1,600 m) visibility and a 300-ft overcast. The pilot decided to conduct the instrument landing system (ILS) approach to Runway 24.

Recorded radar data showed that the Navajo crossed the final approach fix 800 ft above the glideslope. The airplane subsequently was 250 ft above the glideslope when radar contact was lost 3.2 nm (5.9 m) from the runway. “Although the airplane remained within the lateral limits of the approach localizer, its last two recorded radar returns would have correlated with a full-downward deflection of the glideslope indicator in the cockpit,” the NTSB report said.

“Further interpolation of the radar data revealed that, during the last two minutes of the accident flight, the airplane’s rate of descent increased from 400 fpm to greater than 1,700 fpm, likely as the result of pilot inputs,” the report said.

The pilot and his passenger were killed, and the Navajo was destroyed when it crashed in a wooded area about 1 mi (1.6 km) from the airport. The NTSB concluded that the probable cause of the accident was “the pilot’s decision to continue an unstabilized instrument approach in [IMC], which resulted in controlled flight into terrain.”

Truck Driver Tries to ‘Beat’ a Baron

Beech 58 Baron. Destroyed. One minor injury.

The pilot said that he transmitted the appropriate radio calls during a visual approach to Ingleside, Texas, U.S., the night of June 26, 2017. After the Baron touched down, the pilot saw a truck nearing the runway.

“The pilot observed the truck hesitate and then cross the runway towing a large trailer,” the NTSB report said. “The pilot swerved the airplane to the left to avoid impacting the trailer, but the right wing impacted the trailer.” The pilot sustained minor injuries during the collision but was able to exit the Baron before it was destroyed by fire. The truck driver was not hurt.

“The pilot reported that, after the collision, the truck driver apologized and stated that he thought he could ‘beat’ the airplane across the runway,” the report said.

Stall on Departure

Piper Aztec. Destroyed. One fatality, two serious injuries, one minor injury.

The pilot had 20 flight hours’ experience in the Aztec and had completed training for the charter operator nine days before preparing for a flight with three passengers from San Juan, Puerto Rico, to Isla de Culebra the afternoon of June 3, 2017. “The majority of the pilot’s multiengine experience was in a larger airplane with more powerful engines,” the NTSB report said.

The pilot told investigators that he rotated the Aztec for takeoff at 85 kt. He then maintained that airspeed during initial climb. The report noted that because the outer scale on the airspeed indicator showed miles per hour and the inner scale showed knots, the pilot likely rotated at and maintained 85 mph rather than 85 kt. “But either airspeed was significantly less than the airplane’s best rate-of-climb speed of 120 mph (102 kt),” the report said.

The airplane climbed only about 100 ft and then yawed left. “It is likely that the airplane climbed at [85 mph] until out of ground effect but then could not maintain a climb and began to descend back into ground effect,” the report said. “Further, the airplane was not equipped with counter-rotating engines to offset the left yaw at slower airspeed, and the airplane began to yaw to the left.

“Rather than lower the nose, correct for the yaw and continue straight into a 15-kt headwind to increase airspeed, the pilot allowed the airplane to continue to yaw left and exceeded the airplane’s critical angle-of-attack, which resulted in an aerodynamic stall and subsequent descent into water.”

One passenger was killed, the other two passengers were seriously injured, and the pilot sustained minor injuries. Investigators found that the Aztec was within weight-and-balance limits and that no mechanical malfunctions had occurred before the crash.

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Helicopters

Inadvertent Pedal Input

Airbus AS350. Substantial damage. No injuries.

The helicopter was on a portable pad attached to a tug when the pilot prepared for a flight from McAllen, Texas, U.S., on June 17, 2016. He was conducting an engine run-up when he noticed that the right rear door was not closed properly.

“The pilot unhooked his shoulder harness to reach back to secure the door,” the NTSB report said. “While attempting to reach the door, the pilot … inadvertently applied right tail rotor pedal, which caused the helicopter to spin right multiple times.”

The vertical stabilizer was substantially damaged when the AS350 moved off the pad and struck the tug. The helicopter came to a stop upright. The pilot and his passenger were not hurt.

Carburetor Ice Chokes Engine

Robinson R22 Beta. Substantial damage. No injuries.

The R22 was among five helicopters engaged in transporting vacationers between hotels in Norway. The helicopter was last in line during a flight from Forde to Sognefjorden the afternoon of June 14, 2016. It was flying along a fiord at 3,000 ft when the pilot initiated a climb to clear higher terrain.

When the pilot leveled off at 3,800 ft (100 ft above the terrain), the engine began to lose power. The low rotor speed warning then activated, and the pilot attempted to land on a flat area that was clear of snow.

“Due to the reduced engine power, the landing was hard,” said the report by the Accident Investigation Board of Norway. “The left landing gear broke, and the helicopter capsized towards the left. The rotor hit the ground, and the helicopter sustained major damage.” The pilot and his passenger were not injured.

Examination of the helicopter revealed no faults that could have caused the engine malfunction. However, investigators found that the carburetor heat handle had not been engaged and that the environmental conditions in which the R22 was being flown posed a risk of serious carburetor icing. The pilot confirmed that he had chosen not to use carburetor heat.

The report included the following guidance from the R22 Pilot’s Handbook: “Even in generally dry air, local conditions such as a nearby body of water can be [conducive] to carburetor ice. When in doubt, assume conditions are [conducive] to carburetor ice and apply carb heat as required.”

Blown off a Platform

Bell 407. Substantial damage. One serious injury.

Shortly after landing the helicopter on an oil platform in the Gulf of Mexico the morning of June 28, 2015, the pilot noticed that weather conditions west and north of the platform were deteriorating. He decided to depart from the platform.

“He had initiated the [engine] start sequence when a strong wind gust struck the platform and pushed the helicopter off the raised helideck into the water,” the NTSB report said.