Safety call after jet's plunge over Norfolk
Air investigators have called for improved safety procedures after an Easyjet Boeing 737 plunged 9,000ft over Norfolk.
It happened west of Norwich in January 2009 during a post-maintenance check flight.
There was confusion between the two pilots, the Air Accidents Investigation Branch (AAIB) report said.
It has made recommendations to Boeing and to the European Aviation Safety Agency.
In the report, which catalogues what happened when the plane plunged suddenly, the AAIB said the co-pilot had received "no formal training" to conduct such a flight.
'Lack of communication'
It also said various elements of the flight "demonstrated practices which would have been deemed unacceptable in normal operations".
The report said that when things started going wrong on the flight, there was "a lack of any kind of communication" between the pilots and the two observers for more than a minute and 15 seconds.
The report added that the co-pilot "only realised something was wrong" when the captain made an emergency PAN call - one stage down from a Mayday call.
The AAIB said one of the observers had been seated on a storage cupboard behind the captain's seat and was not restrained by a safety harness.
The report questioned the overseeing of post-maintenance and customer demonstration flights, saying that airlines had "few options other than to devise their own demonstration schedule".
The report said that a number of safety actions had already been taken since the incident.