MDA on FCU in A320
 

I just noticed a recent change in limitations of A320.

the AP or FD in OP DES/DES mode can be used in approach if FCU altitude is set to or above, the higher of : MDA or 500ft agl

I always believed that MDA can't be set on FCU. but looks like airbus has no objection in doing so..

Any thoughts about it?

Why would you ever do this ?

Its not that I want to do this. Its about how come Airbus changed its stand and allowed MDA to be set on FCU

Are you sure this was a recent change? Our FCOM has been like this for several years ( at least ). Remember this is a Limitation not standard operating procedure.!

Does not sound like a change to me either. Besides, what they say is that it must not be set below MDA, not that it is a suggested operating technique to do so.

This is not new change in limitation. It was there in FCOM from 18Mar 2011. The use of OP DES/DES upto 500ft is a limitation of the AP/FD equipment. Setting MA on the FCU is the recommended procedure for the NPA.The reason for that is not the limitation but the nature of OP DES mode where it maintains the speed and not the flight path. With terrain clearance issue FPA or VS mode is safer option.

really? can you please give FCOM/FCTM reference for setting minima on the FCU for NPA? how would you set GO AROUND ALT ?

Sorry! I meant Setting MA on the FCU. I corrected the post. Also if you set minimums then aircraft will flare out to level and the minimums will be reached further away closer to the runway.

The previous FCOM minimum height for autopilot use were:

Straight-in non precision approach.....applicable MDA (MDH)
Straight-in LNAV/VNAV approach.......applicable DA
Circling Approach............................applicable DA -100ft

Airbus has recently completed re-certification, and the new limitations are as follows:

Non precision approach using F-LOC or F-G/S.....200' AGL
Non precision approach using FINAL APP,
NAV FPA, NAV V/S, TRK FPA or HDG/VS.............200' AGL
Circling Approach............................................500' AGL

The new limitations allow for greater flexibility on approaches with high minima and on RNAV (RNP) approaches with radius to fix legs at low altitude. Go Around with AP is now also available below minima. In essence, there is now a decorrelation between AP/FD disconnection and the decision to continue.

However, there is a caveat: AP/FD may be kept on below minima, if there are sufficient visual references, and ONLY IF guidance is fully managed, using one of the following modes: APP DES, FINAL APP, F-LOC or F-G/S. AP may therefore logically not be used below minima using NAV or TRK FPA.

It is for this reason the note regarding setting of the FCU altitude at or above the higher of the two: MDA/MDH or 500' AGL. Since this is only applicable to guidance other than fully managed, your company may have to amend procedures for non-precision approaches under these circumstances.

Below minima, visual reference remains the primary reference.

If you want more info, drop me a PM, and I'll forward you a pdf version of a slideshow presented by Airbus on the topic at the last Operations and Training seminar

The topic is about use of FD/AP in OP DES/DES in approach which is not airbus practice. The use/behaviour of autopilot below minima depends on the MSN.