In recent weeks, Apple Inc.’s self-driving car project has lost three more key engineers.

Eric Roges, who Apple appointed as chief engineer for radar systems on the project in question, has left the company in recent weeks to join flying taxi startup Joby Aviation Inc. Alex Clarabur, one of the team’s engineering managers for the battery systems group, moved to Archer Aviation Inc., another company in the air taxi development business.

One of Apple’s hardware engineering managers, Stephen Spiteri also left the company and joined Archer. Joby and Archer confirmed the assignment, highlighting aerospace startups’ efforts to recruit talent from Silicon Valley. Apple did not comment on the matter.

This migration shows the challenges Apple faces in opening up to new industries. In this seven-year-old project, frequent staff departures and strategy changes occurred.

These latest departures come after the loss of at least six employees from the project’s management team this year, including the former head of the team, Doug Field. Among the most notable of the recent departures is Michael Schwekutsch, who heads the software engineering part of the project. Schwekutsch also joined Archer as senior vice president.