Baro/radio altimeter reference index bugs

[Gryphon]

I’d like to know your SOP,s to set the baro/radio altimeter index bugs, when not in use for setting minimuns (MDA/DA/DH) due to the approach category: visual, non-precision, CAT I, CAT II, CAT III.

What reasons do we have to set baro/radio altimeters bugs to that selection?

Thanks a lot.

[Old Smokey]

Gryphon,

In the aircraft I fly (B777), we don't have MDA/DA/DH bugs, they are set electronically, but the function is the same as the manual bugs.

Our SOP is to set them before flight for a possible early return to the departure airport, and then "blank" them until, pre-descent, set them for arrival.

That's the SOP, in an unofficial but useful way, many crews set them to the en-route MEA in case of emertgency descent if MEA is above 10000 feet, e.g. for an MEA of 14500 feet, 145 is set. Useful in the urgency of an emergency descent when finding it from other sources would be a significant distraction.

Other than that they stay blanked out, and memory serves to tell me that they were parked at the 12 o'clock position when en-route on previous aircraft that had these bugs.

Best Regards,

Old Smokey

[The Greaser]

We set the baro bug on departure for single engine flap retraction altitude (normally 1000' aal). And then for approach minima. Other than that, nought!

[Gryphon]

Sorry about that, but what I’d really like to know is if you have a baroaltimeter approach minimums (visual, non-precision, CAT I) what do you set on radioaltimeter DH index?

And if you have a radioaltimeter approach minimums (CAT II, CAT III) What do you set for the baroaltimeters bugs?:O

[BOAC]

Gryphon
1) -20
2) CatI minima for reversion.

[The Greaser]

The 737-300, the radio bug has to be selected below 0 or it is displayed on the EADI. Unless an approach is flown that requires reference to a radio decision height then this is undesirable. So (as BOAC) says the radio bug can be set down to -20, although in reality if it is set to -1 it will make no difference it still will be hidden from view.

If a CAT II/III is being flown, then Radio bug will be set to the appropriate DH eg. 50' and the baro bug will in this case be set to the CAT I DA.

[alf5071h]

Anyone set the RA bug to 250 ft for NPAs as an additional safety check?
Both TERPS and PANS-OPS procedures assure 250 ft obstacle clearance and all MDAs should be above that.
Thus a 250 ft alert before MDA would indicate that there is an error either in navigation or altimetry; below MDA then at 250 ft the aircraft should be within 1 nm of the runway, another good check to alleviate descents into a ‘black hole’.

[BOAC]

As ever, alf - a good idea:ok: