A320 unreliable speed . . . only if you are a nerd like me
Hi all,
An interesting knowledge gap came up during my sim program at my new employer.
I have seen unreliable speed simulated several times throughout the years on the 320/330 but the exercise has always been the result of ADR faults resulting in loss of speed info (red speed tape on PFD)requiring pitch and power to continue safely flying. Not difficult.
Yesterday I went in to the sim armed with what I thought was sufficient knowledge to cope with the unrel speed exercise but I was wrong.
The instructor simulated blocked pitot tubes at 330 knots climbing thru F150 that went undetected by the ELAC’s and FAC’s. 2 ADR’s gave subtly false IAS and only one gave correct.
Of course the incorrect (Cap) side increased into the red and because the fault was undetected the aircraft remained in normal law and gradually pitched up despite our efforts to lower the nose. At no time did it fault the ADR’s and trigger alt law.
I was under the impression that the speed discrepancy would be detected immediately and the ELACS would trigger the NAV ADR disagree followed by altn law as per the wording of the FCTM.
But in this situation the only exit strategy would have been to switch all 3 ADR’s off almost immediately, BEFORE consulting the QRH. The event unfolded very quickly and my efforts to do the right thing by the QRH got us into trouble.
Can this really happen where a speed difference of 30-40 knots can be undetected and put the crew into a situation where normal law refuses you the ability to manage the pitch attitude?
Regards