Ver­ti­cal Aerospace’s inves­ti­ga­tion into a flight test inci­dent on 9 August has iden­ti­fied the root cause to be a fault with a pro­peller. This ear­ly gen­er­a­tion pro­peller had already been redesigned pri­or to the inci­dent, with the issue ful­ly resolved ahead of the next phase of test­ing. Fur­ther rec­om­men­da­tions by the inves­ti­ga­tion are being imple­ment­ed by Ver­ti­cal.

Ver­ti­cal founder and CEO Stephen Fitz­patrick com­ment­ed: “We are pleased with our flight test progress to date and the data, insights and invalu­able learn­ings we have col­lect­ed.

“While a fault of any sort is dis­ap­point­ing, it is not whol­ly unex­pect­ed at this stage of test­ing a nov­el air­craft. I am pleased that as a result of our expert team we have iso­lat­ed the cause of the fault and been able to pro­vide the AAIB with our report with­in 14 days of the inci­dent.

“Our planned sec­ond upgrad­ed pro­to­type, which will include most of our top tier part­ners’ tech­nol­o­gy, will have us in the air ear­ly next year and we remain on track for our cer­ti­fi­ca­tion time­lines”.

Dur­ing one of these test flights, an unex­pect­ed fault occurred caus­ing the air­craft to enter a sta­ble descent, before being dam­aged on impact with the ground. Ver­ti­cal com­plet­ed a swift and thor­ough inves­ti­ga­tion and sub­mit­ted a report to the Air Acci­dents Inves­ti­ga­tion Branch (AAIB).

One of the aircraft’s elec­tri­cal propul­sion units (EPU) had been inten­tion­al­ly dis­abled and one of the front pro­pellers con­nect­ed to a sep­a­rate EPU was released, result­ing in an exces­sive out of bal­ance load, which caused the fail­ure of one of the sup­port­ing pylon struc­tures.

Vertical’s Core pro­pri­etary tech­nol­o­gy unique to the air­craft, includ­ing the high volt­age and bat­tery sys­tems, was said to have ‘per­formed well dur­ing the inci­dent’. Volt­age, cur­rent and pow­er all stayed with­in accept­able lim­its and cell tem­per­a­tures were con­sid­ered nor­mal dur­ing and after the inci­dent.

Vertical’s inves­ti­ga­tion iden­ti­fied the root cause to be a bond­ing issue with­in the pro­peller blade itself. This gen­er­a­tion pro­peller design will not fea­ture on any future VX4 pro­to­type and pri­or to the inci­dent, it had already been redesigned and man­u­fac­tured with a dif­fer­ent process. The air­craft involved in the inci­dent will be used in fur­ther ground tests but will not be repaired to an air­wor­thy stan­dard.

Ver­ti­cal has con­tin­ued fur­ther uncrewed flight tests fol­low­ing the com­ple­tion of the remote thrust­borne flight test cam­paign. The pur­pose of these was to under­stand how the air­craft per­formed out­side of its expect­ed oper­at­ing con­di­tions before the aircraft’s planned retire­ment.

Ver­ti­cal intends to pro­vide a fur­ther full update on the inci­dent once the AAIB’s inves­ti­ga­tion has con­clud­ed. The VX4 cer­ti­fi­ca­tion pro­gramme remains on track with no changes to time­lines.

The assem­bly of a more advanced full-scale VX4 pro­to­type is under­way at GKN Aero­space, and expect­ed to be ready to fly ear­ly next year. Its com­po­nents will include tech­nol­o­gy from most of Vertical’s cer­ti­fi­ca­tion part­ners: Hon­ey­well, GKN Aero­space, Han­wha, Solvay, Leonar­do and Moli­cel.

An addi­tion­al, iden­ti­cal full-scale air­craft has also now been approved and will require rig­or­ous reg­u­la­to­ry over­sight, includ­ing a Per­mit to Fly from the UK Civ­il Avi­a­tion Author­i­ty, to progress to pilot­ed fly­ing.

Ver­ti­cal Aerospace’s exper­i­men­tal pro­to­type air­craft crashed dur­ing a test flight at Cotswold Air­port, home to Vertical’s flight test cen­tre. The com­pa­ny con­firmed the air­craft was remote­ly pilot­ed and there were no injuries dur­ing the acci­dent.