Nearly 400 Max jets were in service worldwide when they were grounded, and Boeing has built and stored about 450 more since then. All have to undergo maintenance and get some modifications before they can fly. Pilots must also undergo simulator training, which was not required when the aircraft was introduced. Hansman said pilot training for qualified 737 pilots shouldn't take long because Boeing has fixed problems with the Max's software. It no longer automatically points the plane's nose down repeatedly, and doesn't override commands from the pilot, according to Boeing.