Story ID: 004
Accidents: April 2021
By: David Jack Kenny
Caption: Preliminary and final accident reports, April 2021
Word Count: 1620
Preliminary Reports
Conquest Down in Tennessee

Cessna 441, February 7, 2021, Winchester, Tennessee – A Cessna Conquest II crashed on approach to the Winchester, Tennessee, Municipal Airport, killing the airline transport pilot and commercial pilot on board.  The IFR flight from the Thomasville, Georgia, Regional Airport checked in with Bowling Green Approach Control while descending to 4,000 feet msl and was cleared for the RNAV approach to Winchester’s Runway 36.  Radar contact was lost as it descended through 2,300 feet, typical for coverage in that area. The controller’s attempt to contact the pilot three minutes later was unsuccessful, and after several hours the wreckage was found along a 500-foot debris path about six miles south of the airport. Both wings and most of the fuselage were consumed by a post-crash fire.

Four Casualties in Virgin Islands Helicopter Crash

Bell 206B, February 15, 2021, St. Thomas, U.S. Virgin Islands – Three family members and a celebrated island pilot were killed when their helicopter crashed during a planned 17-minute sightseeing flight over the island.  A fourth passenger listed on the flight manifest was later confirmed not to have been on board. A witness filmed the helicopter fly out over the ocean and back towards the hill where he stood.  About six seconds after he began filming, “a puff of dark smoke emanated from the vicinity of the engine compartment.” The helicopter abruptly yawed left, then right, and descended into the forest downhill from the witness’ location.

The wreckage was located in steep, heavily wooded terrain. The majority of the cockpit, cabin, and flight controls were consumed by fire, which also damaged “the landing skids, main rotor system, main rotor drive system, engine, hydraulic system, and the forward portion of the tail rotor drive system.” The impeller inducer showed “evidence of hard body FOD ingestion,” and all blades on the fourth-, fifth-, and sixth-stage compressor wheels had been fractured near their root ends and were not found.

The Virgin Islands Daily identified the pilot as Maria Rodriguez, co-owner of Caribbean Buzz Helicopters. The lifelong St. Thomas resident had been named the Helicopter Association International’s 2017 Appareo Pilot of the Year in recognition of her tireless efforts in response to Hurricanes Irma and Maria, flying relief missions for 28 consecutive days. 

Six Mexican Officers Killed in Learjet Crash

Learjet 45XR, February 21, 2021, El Lencero Airport, Xalapa, Veracruz, Mexico – A Learjet operated by the Mexican Air Force crashed while attempting to take off on a training mission, killing all six of the officers on board. Unconfirmed reports suggest that the jet failed to gain altitude and crashed off the end of the runway, igniting a fire that consumed most of the aft portion of the fuselage.  Firefighters and soldiers responded to the scene but were unable to extricate the crew.

The accident occurred just 40 minutes after the 2007-model jet, which had been acquired from a private owner in the U.S., had arrived after an uneventful flight from Mexico City.
Final Reports
Compressor Blade Failure Leads to Multiple ADs

Cessna 208B, November 16, 2016, Solomon Airport, Western Australia – The ATSB traced the fracture of a compressor turbine blade after just 1.8 hours of operation to the installation of a reworked compressor turbine vane ring whose configuration differed significantly from Pratt and Whitney Canada’s (PWC’s) specifications. The vane ring had been repaired by Southwest Turbine Inc. (STI) using a procedure approved by the U.S. FAA as specification no. STI 72-50-254, which involved replacing much of the part’s original structure with a casting manufactured by STI. Testing by the PWC Airfoil Laboratory found that those discrepancies caused airflow distortions that increased vibration of the compressor turbine blades by as much as 200 percent, exceeding design specifications and inducing fatigue cracking that resulted in one blade’s separation from the turbine. The engine failure caused by the resulting cascade of internal damage necessitated an emergency landing on an unpaved mine road, which was executed without injury to any of the 11 passengers on board or either of the two pilots.

The accident occurred on the return leg of a charter circuit rotating workers to and from the Solomon Hub mining center. The outbound flight from Karratha, Western Australia landed at about 07:10 local time.  The return flight took off at 07:43.  Climbing through 4,600 feet over the Hamersley Range, the pilots heard a “loud bang” and “grinding noise” followed by billows of blue and white smoke from the exhaust stack and instrument indications of an engine failure. The pilot-in-command immediately lowered the nose to maintain the best glide speed, determined that the airplane was unlikely to clear the hills between its present position and the airport, and identified an emergency landing site.  The safety pilot activated the Caravan’s Spidertracks emergency notification system and broadcast a Mayday broadcast on the Solomon Airport’s advisory frequency, which was received and relayed by a departing Qantas flight. The passengers were evacuated without incident.

STI responded to the investigation findings by ceasing all repairs of compressor turbine vane rings for PT6A-114A engines. Two weeks later, PWC released Service Instruction Letter PT6A-252 warning of potential compressor blade failure in engines with vane rings repaired under “non-PWC approved processes,” and on August 19, 2019, Transport Canada issued AD CF-2019-30 requiring the replacement of STI-repaired vane rings within 9 months or 240 hours of operation. Canada’s Civil Air Safety Authority automatically adopted the AD, and on August 17, 2020, the U.S. FAA issued a Notice of Proposed Rulemaking advocating adoption of the same AD. The period for public comment on that proposal closed on October 1, 2020.

“High-Risk” Behavior Caused Trimotor Crash

Junkers Ju 52/3m g4e, August 4, 2018, Flims, Grisons Canton, Switzerland – The Swiss Transportation Safety Investigation Board (STSB) found that multiple operational and risk-management deficiencies contributed to the catastrophic crash of the vintage Junkers trimotor on the return flight of a two-day air tour.  All 20 people on board, including 17 passengers and a flight attendant as well as the two highly experienced airline transport pilots, perished when the 79-year-old airplane crashed into a high-altitude mountain valley in a near-vertical nose-down attitude.  The STSB determined that the pilots, who had more than 40,000 hours of combined flight experience, chose to operate the airplane too close to the ground to allow recovery from an upset and close to stall speed in high-density altitude over steep mountainous terrain in atmospheric conditions conducive to turbulence.  The trimotor’s center of gravity was aft of rear limits, further compromising controllability, due in part to errors in both the weights and associated arms entered into the operational flight plan.

Detailed reconstructions based on multiple sources including radar tracks, GPS data, and images recorded in flight by passengers showed that during both the previous day’s flight from Dübendorf Air Base to Locarno Aerodrome and the accident flight itself, the airplane came within 50 meters (165 feet) laterally of rock faces and as low as 120 meters (400 feet) above mountain passes.  Passenger pictures taken just before the crash showed it flying well below the tops of the valley walls; its altitude was subsequently estimated as 125 meters (415 feet) above the Segnes pass. 

In the next 20 seconds, it began to descend in a nose-high attitude. The difference between the Junkers’ pitch attitude and flight path exceeded 20 degrees before it began an uncommanded left roll that was not arrested by significant right aileron. The pilot flying then put in the left aileron in an apparent attempt to make a left turn.  The nose dropped as the bank angle continued to increase and the airplane reached a near-vertical attitude prior to impact.  The STSB noted that the Ju 52/3m is a relatively low-performance airplane, with power loading between that of the Cessna 152 and Piper Super Cub.

Loose Hose Connection Brought Down JetRanger

Bell 206B3, May 21, 2019, 107 km southwest of Jabiru, Northwest Territory, Australia – A loss of engine power during a low-altitude wildlife control flight was caused by a loose connector securing the engine reference air line between the power turbine governor and accumulator, causing the engine to roll back to idle during a low-altitude wildlife control flight. The pilot, spotter, and marksman all suffered serious injuries when the helicopter struck a tree during an attempted emergency landing in a small clearing from about 50 feet above ground level. 

The power turbine governor had been replaced during maintenance operations five days and 4.7 flight hours before the accident. Though both ends of all lines connected to the generator are normally loosened to facilitate replacement, the engineer who performed the work told ATSB investigators that this was not necessary, and insisted that the reference air line’s connection to the accumulator was never touched during the May 16 maintenance session. However, he also acknowledged that interruptions and distractions were common at the maintenance facility.

The accident occurred 44 minutes into a flight to round up and shoot feral horses (an invasive species in Australia) in Kakadu National Park. After confirming that the throttle was still open, the pilot recognized the situation as an emergency and initiated an autorotation to the nearest clearing. The helicopter landed hard after striking the tree, temporarily knocking the pilot and marksman unconscious. The spotter was able to contact park rangers by radio, and a Royal Australian Air Force C-130 operating nearby located the wreckage after the ELT signal was detected by the Joint Rescue Coordination Centre. A precautionary closure of the fuel supply in Jabiru, the last place the accident helicopter had refueled, delayed the EMS helicopter, and the crew finally reached the hospital in Darwin about nine hours after the accident.