Cessna 208B N10JA

Summary

On 24 February 2022 at about 20:45 local time, a Cessna 208B registered N10JA, operated by GoJump, was involved in an accident near Oceanside, California, United States. 2 people were on board and 2 were seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

24 February 2022 at 20:45

Classification

Accident

Location

Oceanside, California, United States

Nearest airport

Bob Maxwell Memorial Airfield (OKB)

Coordinates

33.2204, -117.3432

Aircraft

Cessna 208B

Registration

N10JA

Category

Airplane

Year built

2002

Engines

1

Operator

GoJump

Operating rule

Part 91: General Aviation

Purpose of flight

Skydiving

Phase of flight

Not recorded

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR22LA114

2 people were seriously injured.

The pilot’s intentional inflight operation of the propeller in beta, which led to an aerodynamic lock, his inability to restore forward thrust, and subsequent collision with terrain.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The pilot was performing skydiving operations in the turboprop-equipped airplane. During the fourth flight of the day, after the skydivers departed the airplane, the pilot initiated a steep, turning descent with the power at idle, during which the airplane reached a maximum descent rate of 6,400 ft per min (fpm). While the airplane was on the base leg of the traffic pattern, the pilot attempted to arrest the descent by adding power; however, the engine did not respond to his movements of the power lever. He moved the propeller speed lever, which was also had no effect. He applied full nose-up trim and pulled the control yoke full aft against the stop, but the airplane would not maintain a level attitude, and subsequently collided with terrain short of the runway in a nose-low attitude. There were numerous publications from the STC holder and the engine and propeller manufacturers warning pilots to not use beta mode during inflight operations unless it is certified for those operations. If the power lever is placed below the flight idle gate into beta mode while inflight, the blade position will move to a fine blade angle. Depending on propeller rpm and flight speed, this adjustment may cause the moment from the aerodynamic load on the blade to shift from coarsening to fining, and may result in the propeller blades entering reverse and remaining “aerodynamically locked” in that position. No power lever input from the pilot can alter this, and using the feather valve is ineffective. It is likely that the only viable option to unlock the propeller is to shut down the engine to reduce the moments locking the propeller in place, given it could overcome windmilling speed loads on the blades. Postaccident examinations revealed no evidence of a mechanical malfunction with the engine, propeller, or airframe. A bench-flow test and subsequent teardown examination of the propeller governor revealed a few test points outside of limits that would not have precluded normal governor operation. The propeller rigging was incorrect and it is unknown if the rigging was changed on purpose to aid with faster descent rates; if this was the rigging at the time of the accident flight, it would have contributed to entering an aerodynamic lock sooner. A performance study of the flight based on Automatic Dependent Surveillance – Broadcast (ADS-B) data revealed high negative thrust values that can only be achieved with the power lever below the flight idle gate. It is likely that the propeller blade pitch angle was in beta and that the aerodynamic moment on the blades had reversed, locking the propeller in place and preventing the pilot from recovering control of the propeller.

Quoted verbatim from the NTSB record.