Boeing says its new 787 is beginning the final phase of flight testing and repeated that it should be ready for delivery in August or September.
The final flight testing includes simulations of abnormal operations.
It also tests long-range flying, including the 787's ability to divert to a far-away airport on just one engine.
Federal authorities have special rules for two-engine planes that fly more than an hour away from a suitable landing field. Generally, such flights are over water. The idea is to make sure the plane can make it to an airport if one engine shuts down.
The testing will be done on a 787 with Rolls Royce engines. Separate tests will be done later on 787s with General Electric engines.
Shares of Boeing were last slightly higher in premarket trading.