Hi
Is their any BA 744 drivers out that can answer my questions please.
I have noticed that ba 744 have the own gpws callout "50 above and decide" so if i were flying approach EGLL 27L Baro set to 280 would i get the 50 above at 320 then decide at 280 and if it were set to radio or DH (i think there the same thing) at 200 would i still get these callouts?
B8Z
eckhard
12th Oct 2011, 11:16
Hi B8Z,
You are partially correct. There are two possible DA(H) alert settings:
1. The 'baro' DA setting is referenced to the baro altimeter. The DA that has been set appears as a green line 'bug' on the altimeter tape.
2. The 'radio' DH setting is referenced to the radio altimeter and appears as a numerical value above the radio altimeter numerical read-out. Below 1000ft radio, the read-out changes to a 'clock' display, with the DH appearing as a 'bug'.
It is therefore possible to have two seperate alerts set; however, there will only be one set of audio call-outs.
The '50 above' and 'decide' calls will be made according to the selection of the Captain's DA(H) selector. If his selector is in the 'baro' position, the alert calls will be made with respect to the baro DA. If the Captain's DA(H) selector is in the 'radio' position, the alert calls will be made with respect to the radio DH. The position of the First Officer's DA(H) selector has no effect.
During a normal non-precision or ILS Cat I approach, the radio DH is set below zero (i.e. it is wound 'out of view') and the baro DA is set according to the published minimum. At LHR, the minimum is 280ft baro, so the '50 above' and 'decide' calls will occur at 330ft QNH and 280ft QNH respectively.
On a Cat II or Cat III ILS approach, the baro DA is set as above, to the Cat I minimum (in case of a failure requiring 'reversion' to the Cat I minima) and the radio DH is set to the appropriate radio DH. Let's assume a Cat III approach with a radio DH of 50ft. As long as the Captains DA(H) switch remains in 'radio', there will be no alerting as the aircraft descends through 280ft QNH. The '50 above' call will occur at 100ft radio and the 'decide' call will occur at 50ft radio.
In the case of a 'Cat III no DH' approach, there is no decision height, so the radio DH is wound down out of the way, as in a Cat I approach. The baro DA is set as before to 280ft QNH. The Captain's DA(H) selector remains in 'radio'. There is no alerting as the aircraft passes through 280ft QNH and because no radio DH has been set, there is also no alerting before the aircraft touches down.
Hope this helps!
Eck