Airbus runway overrun protection fault inhibited when the systems is deployed, is it logical?


The Runway Overrun Protection System (ROPS) is designed to alert the flight crew in the case of potential runway overrun situation. The overrun warning (ROW) function automatically arms at 400ft AGL and works until start of braking. The Runway overrun protection (ROP) works from start of braking until the aircraft stops. The surprising part is that the ROW/ROP LOST fault which is triggered when the ROW/ROP is lost is inhibited below 800feet on the final approach till the aircraft decelerates to 80 kts speed. I am comparing the functionality of the Predictive Wind-shear System, the precursor to a wind-shear and with a front running system which gives a reactive wind-shear warning. The predictive wind-shear system fault is not inhibited on final approach.Effectively, the pilot is unaware of any fault in the system, if it may occur below 800feet, when the system is expected to be deployed and functioning. Isn’t this giving the flight crew a false sense of safety whereas the system could be functioning or not functioning. I am sure that a lot of thought must have gone behind the logic but definitely worth a discussion.

Safety First (Airbus)

Flight Phases

The Flight Warning Computer divides its functions according to these ten flight phases. In order to improve the operational efficacy, the computer inhibits some warnings and cautions for certain phases flight phases. It does so to avoid alerting the pilots unnecessarily at times when they have high workloads, such as during takeoff or landing.

If a failure occurs in the inhibited phase, the warning is displayed only when the aircraft has exited the inhibited phase and transited to the non-inhibited phase.

Airbus A-320

The failure mode is further divided into three levels. There are then priority rules. These decide on when to provide the information to the crew.

Level3: Red warnings along with Continuous repetitive Chime and Master Warning.

Level 2: Amber Caution along with Single Chime and Master Caution.

Level 1: Amber Caution without and audio or chime. There is only an automatic call of the relevant system page on the display.

Normal mode displays systems and memos in accordance with the flight phase. Failure mode displays the procedure and the advisory mode displays only the synoptic along with the drifting parameter.

Most warnings and cautions are inhibited during critical phases of flight (Take-off INHIBIT – Landing INHIBIT), because most system failures will not affect the aircraft’s ability to continue a takeoff and landing. (Airbus FCOM).

Discussion of level of safety

Technically, the aircraft can landing when the ROPS wasn’t installed. However if the ROPS is installed and a RWY TOO SHORT (RED)warning is triggered, the flight crew must perform a go-around. This warns the flight crew that an unsafe situation exists and that the aircraft may be able to land but safety is not ensured. Therefore the inhibition logic is is designed nor to overload the flight crew during critical phases of flight since the failures chisen by Airbus to be inhibited in these phases do not affect the aircraft ability to land. However, when safety is paramount, the aircraft must be able to land SAFELY. Therefore there is a need for discussion of this inhibition of ROW/ROP LOST when the ROPS is deployed.

The Airbus FCTM states that the absence of ROW alert during approach should not prevent the flight crew from monitoring the stabilised approach criteria and perform a go-around if necessary. On the flip side a system designed to ensure safety, if previously working and develops a fault when subsequently, the fault must be displayed. There may not be a Chime or Master Caution but the ECAM must display the failure ( Level 1 Failure mode).

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