[foxmoth]

Doing some formation the other day (ok, some time ago, before lockdown) and asked lead to start a loop at 140kts, as he was going through 160 asked him to ease out the dive - he reported not yet having reached 140 but felt faster, ASI seemed to be reading OK at 90-100 but in error above 120 or so. Ground tested OK to within 3 kts - thoughts?

[Flyin'Dutch']

Static leak/blockage?

[T67M]

Static pipe disconnected and reading cabin pressure?

[riverrock]

So it's going to be pitot pressure too low ( a leak of some sort), static too high (increasing pressure with speed, so getting reading from wrong place or again a leak) or a gauge issue.
Should be able to get to the bottom of it with the right calibrated kit.

[helicopterdcr]

For testing, you could do worse than this:

Despite the slightly annoying slow speech of the presenter (tip: adjust playback speed) it works.

[foxmoth]

Thanks, but checked both pitot and static for leaks.

[Flyin'Dutch']

Thanks, but checked both pitot and static for leaks.

Has the 'thang' itself been checked and calibrated recently. How about the other machina?

[foxmoth]

All ok with the check machine, may have suspected the other aircraft if the pilot in this one had not been wondering a) why it was taking so long to accelerate, and b) why the aircraft felt like it was a LOT faster than indicated.

[RichJordan]

I've got the opposite problem, ASIs all over read by approx 10%. Keep meaning to blow static line through.

[Rob L]

I've got the opposite problem, ASIs all over read by approx 10%. Keep meaning to blow static line through.

If you do, disconnect all instruments first!

To be fair, for a PtF type, any CAA approved shop will undertake a pitot/static check for you for a few hundred quid; good assurance of your instruments, in my opinion. (It's part of the Annual for EASA-CAA-types).

[Rob L]

I've got the opposite problem, ASIs all over read by approx 10%. Keep meaning to blow static line through.

If you do, disconnect all instruments first!

To be fair, for a PtF type, any CAA approved shop will undertake a pitot/static check for you for a few hundred quid; good assurance of your instruments, in my opinion..and you'll get an approval for the airframe logbook. (It's a standard part of the Annual for EASA-types, of course).

[Charliesixtysix]

Doing some formation the other day (ok, some time ago, before lockdown) and asked lead to start a loop at 140kts, as he was going through 160 asked him to ease out the dive - he reported not yet having reached 140 but felt faster, ASI seemed to be reading OK at 90-100 but in error above 120 or so. Ground tested OK to within 3 kts - thoughts?

Problem resolved?
If so, what was the cause of the discrepancy ?

[foxmoth]

Looks like position error - the pitot had moved down possibly due to a missing bolt, doing the permit renewal flight I also found we had a higher than expected stall speed so over reading at the low end.