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Airspeed check against groundspeed (and stabilised approaches)

Do you check the ASI against the GPS groundspeed routinely during an approach?

Negative

EBZH Kiewit, Belgium

No

EDDS - Stuttgart

Nope

EGTK Oxford

No.

LDZA LDVA, Croatia

Hm. Time to begin a sub-group or a counter-forum, meseemeth…

EBZH Kiewit, Belgium

Yes, especially if there’s a tailwind.

Also, when calibrating, we fly a constant power approach (changes in power produce spikes on the graph) and we need to ensure an average groundspeed of 140kts. Consequently, in a nil-wind scenario, we will start a run at 11nm and 3180ft and 100KIAS, abeam the G/P antenna at 182KIAS and over the Localiser at 108KIAS. If there is a wind, we then have to adjust our starting point IAS, thus affecting our G/P and LOC speeds. It can all get rather interesting when flying an approach with a 30kt tailwind!!

Last Edited by Dave_Phillips at 21 May 19:23
Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom

This might also be relevant, although I suspect Fuji is referring to checking the accuracy of the ASI before flying an approach.

Administrator
Shoreham EGKA, United Kingdom

Dave_Phillips wrote:

Yes, especially if there’s a tailwind.

Also, when calibrating, we fly a constant power approach (changes in power produce spikes on the graph) and we need to ensure an average groundspeed of 140kts. Consequently, in a nil-wind scenario, we will start a run at 11nm and 3180ft and 100KIAS, abeam the G/P antenna at 182KIAS and over the Localiser at 108KIAS. If there is a wind, we then have to adjust our starting point IAS, thus affecting our G/P and LOC speeds. It can all get rather interesting when flying an approach with a 30kt tailwind!!

Peter it was partly to do with ASI accuracy and partly to do with a tailwind turning into no wind or even a headwind, and partly to do with landing at airports without a windsock or any ground radio. Dave, I assume you are therefore monitoring the IAS against the GS from teh start of your run? What range of differences have you seen over the course of a run?

I think the worst I have seen is a reported surface wind giving about 7-10kts headwind with a 20kt tailwind at 3000ft. That is not a unique occurrence.

Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom
71 Posts
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