Do you check the ASI against the GPS groundspeed routinely during an approach?
Negative
No
Nope
No.
Hm. Time to begin a sub-group or a counter-forum, meseemeth…
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!!
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.