Europe's certification authority is aiming to introduce requirements to reduce loss-of-control risks during go-around, with particular attention on the problem of somatogravic illusion.
The European Aviation Safety Agency is seeking comment on proposals to ensure new aircraft have design features which do not create an "unacceptable risk" of losing control of the trajectory – and the aircraft as a whole – during a missed approach.
EASA points out that the high level of thrust typically commanded during a go-around is a notable source of this risk.
"When full thrust or power is applied during a go-around, an excessive level of performance may be reached very quickly," it says in its proposal.
"[This] may make it difficult for the flight crew to undertake the actions required during a go-around, especially in a constrained and rapidly changing environment."
High thrust settings generate sudden acceleration and sharp pitch-up moments, and the combination of these – especially in low-visibility conditions – can create somatogravic illusions, a false but convincing impression of the aircraft's attitude. Pilot reactions to this false impression can result in the aircraft's being inadvertently pushed nose-down during a go-around.
EASA points out that Airbus, Boeing and Fokker have already developed systems to limit thrust to a suitable level when the crew executes a missed approach.
"Such a design improvement would also be required from other manufacturers developing [aircraft] that can also present a similar level of risk," says its proposal.
Its revised certification standard would require mitigation measures – such as thrust reduction – should pitch rate rise above 4°/s, pitch attitude increase beyond 20°, vertical speed rise beyond 3,000ft/min or longitudinal acceleration exceed 2kt/s.
EASA's proposition would also require airframers to investigate longitudinal controllability and authority, during go-around and other flight phases, which would contribute to mitigate the risk of upset attitudes – in particular the effect of automatic pitch trim.
"The non-recurring cost of this option is substantial for manufacturers that have not yet developed a mitigation means like a reduced go-around thrust function," it acknowledges.
"However, when included in the development of an [aircraft], this is not significant relative to the overall cost of a development."
EASA's proposal will remain open for comment until 11 August.