NTSB Finally Releases Report on Joby Aviation Crash JAS4‑2 Prototype

It has tak­en two years for a report on Joby Aviation’s JAS4‑2 crash to be pub­lished. Car­ried out by the U.S Nation­al Trans­porta­tion Safe­ty Board (NTSB), the Feb­ru­ary 16th, 2022 acci­dent of a first gen­er­a­tion, pre-pro­duc­tion pro­to­type flight test air­craft, stat­ed the prob­a­ble cause of the crash was “The sep­a­ra­tion of a pro­peller blade dur­ing expan­sion flight test­ing that result­ed in cas­cad­ing effects to include the sep­a­ra­tion of mul­ti­ple propul­sion motor/propeller assem­blies and the loss of remote pilot con­trol of the air­craft.”

There were no injuries. The air­craft was destroyed.

The report states, “Con­tribut­ing to the acci­dent was the tilt rotor actu­a­tor link­age for propul­sion sta­tion 3 that allowed some pro­peller blades to be at a steep­er angle than com­mand­ed.” Adding, “The enve­lope expan­sion flight test con­di­tions were beyond the expect­ed oper­at­ing con­di­tions of the air­craft.” 

(Cred­it: Red­dit)

The acci­dent occurred dur­ing a sec­ond test flight for that day, after reach­ing the max­i­mum dive speed of 181 knots at an alti­tude of approx­i­mate­ly 8,900 ft. A pro­peller blade on propul­sion sta­tion 3 (locat­ed on the right wing inboard) expe­ri­enced a bend­ing fail­ure near its root which cul­mi­nat­ed in the release of the blade.

The report explains, “The released blade impact­ed the pro­peller on propul­sion sta­tion 4 (locat­ed on the right wing out­board), which sub­se­quent­ly result­ed in a release of the impact­ed blade. Cas­cad­ing effects result­ed from the ini­tial inflight blade fail­ures includ­ing the sep­a­ra­tion of mul­ti­ple propul­sion motor/propeller assem­blies and loss of remote pilot con­trol of the air­craft. The air­craft depart­ed con­trolled flight after the ini­tial inflight blade fail­ure and impact­ed the ground about 0.5 nau­ti­cal miles south-south­east away.”

The state­ment con­tin­ues, “Exam­i­na­tion of the High-Res­o­lu­tion Recorder data for the acci­dent time peri­od revealed that the vari­able pitch actu­a­tor for sta­tion 3 was com­mand­ing a typ­i­cal cruise pitch when the blade release occurred, where­as video evi­dence indi­cat­ed a steep­er pitch on some blades imme­di­ate­ly before the ini­tial blade release. Accelerom­e­ter data for sta­tion 3 showed a rapid growth in vibra­tion after reach­ing the acci­dent flights test con­di­tion before the ini­tial blade release. Tilt actu­a­tor posi­tion val­ues for sta­tion 3 also showed an oscil­la­tion at this time.”

The report says that an exam­i­na­tion of pri­or flight test data by Joby revealed “con­sis­tent asym­met­ric behav­iour between sta­tion 2 and sta­tion 3, despite iden­ti­cal mir­rored designs.”

(From the NTSB Report)

In cruise mode, the tilt actu­a­tors on sta­tion 3 showed “increased activ­i­ty in all flight con­di­tions com­pared to sta­tion 2.” Tilt actu­a­tor link­age loads were also high­er in sta­tion 3, which can be “an indi­ca­tion of anom­alous behav­iour in the tilt mech­a­nism.” The res­o­nant response to this pro­peller mode cross­ing in sta­tion 3 was also con­sis­tent­ly stronger than in sta­tion 2, “indica­tive of a cou­pled inter­ac­tion with the anom­alous tilt mech­a­nism.”

It is inter­est­ing to note that the Ver­ti­cal Aero­space VX‑4 crash, last August, was also due to a faulty pro­pel­lor although, to be fair, the Joby pro­to­type was being pushed to its absolute extreme.

Please Read the Full Report

https://t.co/V1ibxoPfRx

(Top image: Joby Avi­a­tion)

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