Brazilian authorities have ordered revision of Embraer EMB-545 and -550 executive jet flight manuals to warn pilots against pitch inputs which could adversely affect the angle-of-attack protection system.
Civil aviation regulator ANAC’s directive – which has just a five-day compliance deadline from 26 February – requires a warning that “rapid and large alternating pitch control inputs must be avoided” if the angle-of-attack limiter is engaged.
It states that such inputs could “prevent or delay” disengagement of the limiter.
This limiter is designed to protect the aircraft from low-speed stall by restricting the aircraft’s maximum angle-of-attack.
It activates if the angle-of-attack exceeds a certain threshold or the indicated airspeed falls below a particular value on the speed tape. In such cases the autopilot disengages and nose-up sidestick inputs directly control angle-of-attack.
But ANAC states that, if the limiter remains active during the landing flare, the pitch response could be reduced.
If the approach is conducted in “unstable air conditions”, it says, this lack of responsiveness could result in a high rate of descent while the aircraft is close to the ground.
ANAC says the directive references a recent US hard-landing event in such conditions that led to “substantial damage”, with the limiter remaining engaged until touchdown.
While the regulator has not specified details, US investigators are probing a September 2023 landing accident involving a Flexjet EMB-545 which began porpoising on approach to St Simons Island airport in Georgia.
The pilot was observed to move the sidestick “back and forth excessively”, says the US National Transportation Safety Board, before remarking that the aircraft was not responding to the control inputs.
It touched down hard, before the threshold, then bounced and skidded along the runway before veering off. Both main landing-gear were damaged, and had punctured the top of the wing.
French investigators had previously probed a hard landing involving a Russian-registered EMB-550 at Paris Le Bourget in November 2017, which occurred when the crew selected an approach speed below the limiter activation speed.
The limiter then prevented the captain from carrying out the flare, and the heavy touchdown caused the right-hand main landing-gear to puncture the wing.
ANAC says the characteristics of the US occurrence “have differences” from the circumstances of the Le Bourget accident.
Along with the pitch-input warning, ANAC’s directive orders changes to the flight manual’s sections on approach speeds and use of the autothrottle. It also contains information stating that, if the angle-of-attack limiter is engaged during approach and prior to flare initiation, the approach should be considered unstable and a go-around initiated.
