Ask Captain Lim

Hi Capt Lim,

On the ground with ADR 2 inoperative, why must takeoff be performed in Config 3 and not Config 1+F?

Thanks

Bob

Hi Bob,

Here is a little about the ADR (air data reference) for the benefit of others - the ADR is a part the ADIRU (Air Data and Inertial Reference Unit) that supplies a lot of vital information through the various sensors (temperature, pitot and static pressure probes, etc) on the body structure of the plane.

There are 3 identical ADRs on the Airbus A320. On a normal flight, only ADR1 and ADR2 are operating with ADR3 on standby.

The Airbus A320 Minimum Equipment List (MEL) states that when ADR2 is inoperative, take off should not be performed using Flaps (Config) 1+F because this may lead to an uncommanded Flap retraction. Why? This is due to the No 2 Flap Channel of SFCC (Slat/Flap Control Computer) inability to cross check the airspeed coming from ADR1 with ADR2 airspeed coming from SFCC No 2 slat channel.

Hope this briefly answers your question (but it may be too technical for others) Hence, my reluctance to answer technical questions in this site.