Prop Separates in Flight

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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Pilots Credited for Safe Outcome

Saab 340B. Substantial damage. No injuries.

The Saab was about 19 km (10 nm) from the destination when the right propeller separated and flew clear of the aircraft. The flight crew performed the pertinent checklist actions, declared an urgency and landed the aircraft without further incident.

The serious incident occurred the morning of March 17, 2017. The Saab was on a scheduled flight from Albury, New South Wales, Australia, to Sydney with 16 passengers and three crewmembers. The aircraft was about 102 km (55 nm) from Sydney when the crew noticed slight fluctuations of the right engine torque indication.

“The captain manipulated the power levers and condition lever to see if that could rectify the condition,” said the report by the Australian Transport Safety Bureau (ATSB). “When those actions were unable to stop the fluctuations, the crew proceeded to action the uncommanded-engine-operation procedures.”

While the pilots were conducting the checklist, they felt slight vibrations that appeared to emanate from the right engine. The vibrations increased, and the first officer saw that the right engine nacelle was shaking. The crew responded by shutting down the engine in accordance with the checklist. While they were performing the procedures, the right propeller separated from the engine. The crew declared an urgency, finished shutting down the engine and landed the aircraft at Sydney Airport.

The propeller had separated when the gearbox shaft fractured about 10 minutes after the pilots first noticed the engine torque fluctuations. The propeller, still mounted to the gearbox shaft flange, was found in a densely wooded area near the airport. “Subsequent laboratory analysis of the propeller shaft revealed that the failure occurred as a result of a [corrosion induced] fatigue crack that had initiated from a propeller gearbox propeller shaft flange dowel pin hole,” the report said.

“The ATSB found that the manufacturer’s maintenance documentation did not include specific inspection procedures to detect fatigue cracking of the propeller shaft,” the report said. The circular gearbox shaft flange is mounted on the propeller shaft, which extends from the engine gearbox. The flange has 14 circumferential holes — two for dowel pins that locate the propeller on the flange and 12 for mounting the propeller with self-locking nuts.

The incident aircraft was manufactured in 1991 and had accumulated 39,625 hours in service. A propeller gearbox assembly with 46,406 hours in service had been installed on the right engine, a General Electric CT7-9B, about two years before the incident.

The report noted that after the incident, the engine manufacturer issued service bulletins requiring immediate and periodic inspections of the propeller shafts on the affected engines.

“This occurrence highlighted how non-life-limited components such as a propeller shaft may still develop defects and fail in flight,” the report said. “Appropriate training, the use of checklists and effective crew interaction provide the best opportunity for a positive outcome in the event of such a failure.”

ATSB credited the Saab pilots’ professionalism and crew resource management for the safe outcome of the serious incident. They “worked together well … did not divert from the checklists … did not make any rapid decisions and ensured that all options were considered before action was taken,” the report said.

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Jets

Cowling Detaches on Runway

Airbus A300, Boeing 767. Minor damage. No injuries.

Visibility at Germany’s Cologne/Bonn Airport was 6,000 m (4 mi) in snow when the A300 freighter touched down on Runway 32R the night of Feb. 9, 2010. The flight crew felt the airplane lurch slightly left when they retracted the thrust reversers as indicated airspeed decreased through 80 kt. “By actuating the control pedals, the airplane was kept on track,” said the report by the German Federal Bureau of Aircraft Accident Investigation (BFU).

After parking the A300 at a stand, the pilots were told by a ground crewmember that the left thrust reverser translating cowling on the right engine was missing. The pilots relayed that information to the airport control tower. However, a 767 had landed on Runway 32R about 12 minutes earlier — two minutes after the A300 landed — and had run through the debris from the A300’s cowling.

The report characterized the damage to both airplanes as minor. In addition to the damage caused directly by the reverser cowling separation, the inner flap drive on the A300’s right wing had been damaged. The 767’s right engine air intake cowling and a wheel on the right main landing gear also had been damaged.

“In the past, thrust reverser cowlings or parts thereof had separated from airplanes,” the report said. “In August 2009, the thrust reverser manufacturer had published a fan reverser service memorandum [recommending] that airplane operators conduct additional checks on thrust reversers in order to prevent age-related malfunctions.”

Faulty Valve Causes Depressurization

Airbus A320. Minor damage. No injuries.

The A320 was cruising at Flight Level (FL) 390 (approximately 39,000 ft) during a flight from Mumbai, India, to Cochin, the evening of Feb. 27, 2017, when the flight crew received an indication that the no. 1 air-conditioning pack was overheating. Shortly thereafter, the cabin altitude began to increase (an indication of cabin depressurization). The crew requested and received clearance from air traffic control (ATC) to descend to a lower altitude.

“Before the descent could be commenced, there was a rapid increase in cabin pressure altitude,” said the report by India’s Civil Aviation Department. The crew declared an emergency, conducted an emergency descent and diverted the flight to Mangalore, where the aircraft was landed without further incident. None of the 58 passengers or six crewmembers was injured.

Examination of the A320’s cabin pressurization system revealed that the flow control valve on the right air-conditioning pack had failed. The report said that the flow of engine bleed air through the left pack was not sufficient to maintain cabin pressurization at FL 390.

Deicing Fluid Causes Apu Failure

Fokker 100. Substantial damage. No injuries.

The Fokker’s auxiliary power unit (APU) was running when a deicing-equipment operator began to spray Type 1 deicing fluid on the airplane at Nuremberg (Germany) Airport the morning of Jan. 20, 2015. He began at the empennage and was treating the right side of the vertical stabilizer when he heard the sound of the APU’s compressor speed increasing.

“He described the noise [as] getting louder and the frequency increasing,” the BFU report said. “Furthermore, the exhaust fumes increased strongly. He then closed the jet tube and ended the deicing process. At that moment, he heard a loud bang and sought cover within the [extended deicing] basket. Immediately afterwards, there was a second, more intense, bang, and the APU shut off.”

The driver of the deicing vehicle told investigators that he saw a maintenance-access door on the bottom of the airplane’s fuselage spring open and emit a flame about 2 m (7 ft) long. “He also stated that the blast waves of the two bangs were so intense that the deicing vehicle rocked,” the report said.

The flight crew felt the airplane shake and saw indications that the APU had shut down automatically. Investigators determined that the APU had ruptured when deicing fluid was ingested and ignited. The Fokker was substantially damaged when the APU’s compressor disk shattered. Some of the debris punctured the pressure bulkhead at the rear of the cabin, but none of the passengers or crewmembers was injured.

The APU is located inside the Fokker’s tail section, behind the aft pressure bulkhead. The report said that the APU air intake has no external markings and can be difficult to see during deicing operations. Based on the findings of the investigation, the BFU recommended requirements for the air intakes on Fokker 100s to be clearly marked.

Compressor Blade Fails

Cessna Citation 560. Substantial damage. No injuries.

The Citation was climbing through FL 320 during a business flight from Brisbane, Queensland, Australia, to Townsville on Jan. 26, 2018, when the flight crew heard several loud bangs emanating from the rear of the aircraft and smelled smoke in the cockpit. They declared an urgency and initiated an emergency descent to 10,000 ft.

Both pilots donned oxygen masks during the descent but did not deploy the passenger masks because the smoke had dissipated. “It was likely that the reduction in power necessitated by the emergency descent eliminated the smell and visual evidence of the smoke,” the ATSB report said.

The crew considered diverting to an alternate airport but decided that their best option was to return to Brisbane. They landed the Citation there without further incident. None of the six passengers or the pilots was injured, but examination of the aircraft revealed substantial damage within one of the Pratt & Whitney Canada JT15D-5D engines (the report does not state which engine).

“Examination of the aircraft in Brisbane revealed that the cause of the loud bangs was the failure of one of the aerofoils [blades] on the LP [low pressure] compressor (boost) stage rotor, which then exited the engine via the usual gas flow,” the report said. “Small globules of molten metal were found in the exhaust [system].” Investigators determined that the aerofoil failed because of a high-cycle fatigue crack of unknown origin.

“The boost rotor on JT15D-5D engines had a history of aerofoil distress, and a number of actions had previously been taken to address the issue,” the report said. “However, as a result of some additional events (including this one), the engine manufacturer commenced further work aimed at a better understanding of the distress mechanism.”

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Turboprops

Rudder Trimmed Full Left

Beech King Air B200. Destroyed. Five fatalities, two minor injuries.

The pilot was conducting a charter flight with four passengers from Essendon (Victoria, Australia) Airport to King Island, Tasmania, the morning of Feb. 21, 2017. The King Air veered left of the runway centerline during the longer-than-normal takeoff roll. After lifting off the runway, the aircraft yawed left and entered a shallow climb. Although ATC had instructed the pilot to turn right after takeoff, the aircraft deviated left of the extended runway centerline in an increasing sideslip and with the landing gear still extended, the ATSB report said.

The King Air climbed about 160 ft before it began to descend. The pilot transmitted seven “mayday” radio calls before the aircraft struck the roof of a building and burst into flames. The passengers and the pilot were killed, and two people on the ground sustained minor injuries.

Investigators determined that the pilot likely had not noticed before initiating the takeoff that the rudder was trimmed full-nose-left. “The position of the rudder trim resulted in a loss of directional control and had a significant impact on the aircraft’s climb performance in the latter part of the flight,” the report said. “This accident highlights the critical importance of appropriately actioning and completing checklists.”

Failure to Yield Right of Way

Cessna 208B. Substantial damage. No injuries.

The pilot was taxiing the Caravan to the ramp at Baltimore/Washington International Thurgood Marshall Airport <that’s what the logo says>the morning of Feb. 24, 2015, after completing a night cargo flight. Recorded security video showed that the airplane’s landing lights, taxi lights, strobe lights and rotating beacon were illuminated. As the airplane neared an intersection between the taxiway and a service road, a ground service vehicle crossed in front of it.

“To avoid a collision, the pilot applied the brakes and used reverse thrust, which stopped the airplane about 3 ft [1 m] from the vehicle,” said the report by the U.S. National Transportation Safety Board (NTSB). “The rapid application of braking and reverse thrust resulted in the airplane rocking backward and the empennage striking the ground, substantially damaging the airframe.”

“State law required that ground vehicles always yield right of way to taxiing aircraft,” the report said. The vehicle driver told investigators that he had been distracted while reaching down to retrieve a security badge and did not see the airplane as it approached the intersection.

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Piston Airplanes

Ice Covers Windshield

Cessna 340A. Substantial damage. No injuries.

Weather conditions along the route were deteriorating, and the pilot performed the before-takeoff checks of the 340 in a hangar in an attempt to expedite the departure from Juneau, Wisconsin, U.S., for a positioning flight to Waukesha, Wisconsin, about 112 nm (207 km) southeast the night of Feb. 24, 2017.

“The weather conditions included low visibility, freezing drizzle and mist,” the NTSB report said. “During the pilot’s [admitted] ‘haste’ to preflight and take off, she inadvertently selected the wrong switch for windshield heat.” As a result, ice subsequently accumulated on the airplane’s windshield, causing the pilot to lose all forward visibility while conducting an instrument landing system (ILS) approach to Waukesha.

“The pilot executed a missed approach and contacted an instructor pilot at the departure airport to confirm the location of the windshield heat switch,” the report said. “The pilot then activated the windshield heat switch, and enough ice melted for the pilot to conduct another approach.”

The pilot told investigators that she conducted the second ILS approach at higher-than-normal airspeeds because the airplane was “carrying a lot of ice.” However, the 340 was unable to maintain altitude, descended below the glideslope and struck terrain short of the runway. The airplane was substantially damaged, but the pilot was not hurt.

Control Lost During Training

Technam P2006T. Destroyed. Two fatalities.

A flight instructor and a pilot taking his first multiengine training flight departed from Calgary, Alberta, Canada, the evening of Feb. 12, 2017, and climbed about 2,500 to 3,000 ft above terrain to practice high-speed and low-speed maneuvers about 32 nm (59 km) from the airport.

Investigators determined that about 30 minutes after departure, a loss of control occurred during an approach-to-stall exercise or an attempted stall recovery. The Technam — a light, four-seat airplane powered by four-cylinder Rotax engines —entered a spin, from which recovery was effected. “However, insufficient altitude remained to recover from the ensuing dive,” said the report by the Transportation Safety Board of Canada.

Recorded ATC radar data indicated that the airplane was descending at 11,200 to 14,000 fpm when it struck terrain in a near-vertical attitude. The airplane was destroyed by the impact and subsequent fire, and both pilots were killed.

Noting that spin testing is not required during the certification of multiengine airplanes, the report said, “The spin qualities of twin-engine aircraft are therefore unknown, and the effectiveness of recovery techniques in use are assumed.” Thus, full-stall exercises during multiengine training pose an increased risk that “pilots may not be able to regain aircraft control if the stall progresses into a spin,” the report said.

Brake Pedal ‘Flops to Floor’

Cessna 402C. Substantial damage. No injuries.

The pilot was conducting his 11th flight of the day— a 35-minute charter flight with eight passengers from St. Thomas, U.S. Virgin Islands, to Virgin Gorda, British Virgin Islands — the night of Feb. 11, 2017. The pilot was familiar with the destination airport. However, the U.K. Air Accidents Investigation Branch (AAIB) determined that, under the existing conditions, the aircraft’s required landing distance at Virgin Gorda was close to the landing distance available on the runway.

“The pilot commenced his approach to Virgin Gorda using his usual turning and configuration points,” the AAIB report said. “The aircraft touched down normally, and the pilot retracted the flaps before applying the brakes.” The pilot told investigators that the brakes initially responded normally, but the left brake pedal then “flopped to the floor.”

“Judging he had insufficient room to abort the landing, the pilot continued to pump the brakes, which he did not consider to be responding,” the report said. “He shut down the engines before the aircraft left the paved surface, struck signage and then a low wall before coming to rest on a bank.” The 402 was substantially damaged, but none of the occupants was injured.

Examination of the brake system revealed several “shortfalls during maintenance,” the report said. The failure of the brake system was attributed primarily to deterioration of a seal in the left master cylinder.

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Helicopters

Driveshaft Coupling Overheats

Bell 206B. Substantial damage. One fatality, three serious injuries, one minor injury.

The pilot was conducting a sightseeing flight along the coast near Honolulu the morning of Feb. 18, 2016, when he felt a vibration throughout the JetRanger’s cabin. He told investigators that he was diverting the flight toward a nearby airport when “the vibration developed into a grinding sensation, which was followed by illumination of the main rotor low-rpm warning light and an increase in engine rpm,” the NTSB report said.

“The pilot said that, about 20 ft above the water, it felt like the main rotor stalled; the helicopter lost lift, and it ‘fell out of the sky,’” the report said. “The helicopter descended rapidly into the water and sank about 20 ft [6 m] from the shoreline.”

Three passengers and the pilot were able to exit the helicopter, but the passenger in the middle of the aft seat was not. Several attempts to extract the passenger failed. “The first responder reported that the passenger’s life preserver appeared to be entangled with the seat belts,” the report said.

Examination of the JetRanger revealed that the forward coupling attaching the engine driveshaft to the transmission had overheated, causing the driveshaft to separate. Investigators found that unrecorded maintenance had recently been conducted on the driveshaft. “It is likely that when this maintenance was conducted, grease was not applied to the forward coupling as specified in the manufacturer’s maintenance manual,” the report said.

Distracted by iPad

Robinson R44. Substantial damage. One minor injury.

Shortly after taking off at dawn on Feb. 24, 2018, and climbing about 300 ft for a business flight from Woodland, California, U.S., the pilot noticed that her iPad was not showing her location. “While attempting to fix the iPad, she inadvertently pushed the cyclic forward,” the NTSB report said. “She reported that when she refocused her attention outside the helicopter, impact was imminent.”

The fuselage and rotor systems were substantially damaged when the R44 struck trees and fell to the ground on its left side. The pilot sustained minor injuries. “The pilot reported … that the accident could have been prevented by not allowing herself to become distracted during flight,” the report said.

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