Airbus has emphasised to pilots that rudder pedals should not be used to counter turbulence- or vortex-induced roll, and to ensure any high-load event is documented and promptly reported.
The airframer has highlighted an incident involving an A320 which, during a climb from 30,000ft to 36,000ft, unexpectedly rolled into a 52° right bank.
Its pilot countered with both the sidestick and rudder pedals.
These combined inputs caused the jet to bank left, and an opposite reaction by the pilot then led the aircraft to bank “severely” to the right, the airframer states.
This cycle then repeated with a further left and right bank before the A320 was stabilised. Over the course of the occurrence, a ‘stop rudder input’ warning was triggered four times.
The aircraft continued climbing to cruise altitude and proceeded to its destination.
But while the crew reported a turbulence encounter to maintenance personnel, they did not mention the rudder input warning, says Airbus in its in-house publication Safety First.
The jet was not equipped with a flight-data interface unit that could trigger a lateral load alert.
Airbus says the event was “not immediately reported” by the crew and remained undetected until routine data analysis – nearly a year later – picked up unusual flight parameters.
The data revealed the A320 was subjected to maximum lateral acceleration of 0.41g, which is considered a “red level event” under maintenance guidance, but the jet was only inspected on the basis of excessive turbulence.
Analysis of the data found that the flight loads had been ”in the vicinity of design limits”, states Airbus, although they “did not exceed them”.
Airbus aircraft are fitted with two types of rudder, either a mechanical system – found on older single-aisle and widebody jets – or an electric rudder, such as that on the A321XLR, A220, A330neo and A350.
Forceful alternating rudder-pedal inputs risk structural damage, says Airbus, even with electric-rudder aircraft whose flight-control laws can reduce stresses.
“[Electric rudder laws] should not be considered as protection against structural damage or failure of the rudder due to such inputs,” it states.
Airbus says use of the rudder pedals should be limited to take-off and landing, crosswind control, and countering yaw from engine failure until the rudder is trimmed.
“Using rudder inputs in other flight phases or during a turbulence encounter may cause unnecessary trajectory deviations and excessive loads on the rudder structure,” it says.
Airbus adds that crews must provide comprehensive information to maintenance personnel if they experience a high-load event – whether caused by turbulence or excessive manoeuvring – particularly if it results in a ‘stop rudder input’ warning.
“This critical information enables maintenance personnel to properly assess lateral loads and conduct necessary inspections, potentially preventing more serious structural issues from developing,” it states.
