fixed HDU and Flt page Displays Ground Speed under approximately 30kts True (Previously thought to be correct but appears not)

[Scaley]

Simple bug - at low airspeeds the HDU symbology and FLT page appear to transition to displaying ground-speed not true airspeed. 

Re-produce by hovering with strong headwind and seeing zero displayed airspeed despite the aircraft correctly measuring the windspeed as shown on the PERF page. Accelerate to above 30kts groundspeed flying directly into the wind and see the airspeed correctly showing as equal to groundspeed+windspeed.

Wind TAS GS.trk

Edited May 4, 2022 by Scaley

[Scaley]

Verified as (on a general level at least) correct by  one of the SMEs. Leaving this here for anyone else who reports the same thing.

See next post

 

Edited May 4, 2022 by Scaley

[Scaley]

So after some more discussion with another few Apache pilots it appears this may actually not be correct as is. Currently one AH-64D pilot has told me the current behaviour is correct but that they had to hunt for a reference in some old documentation, and 2 have told me the current behaviour is NOT correct, and the HDU speed is ALWAYS TAS, with no exceptions. 

The suggestion that the current behaviour is not correct appears to be supported by at least 3 real documents, none of which mention the HDU ever displaying anything but TAS, and all explicitly call the readout "TAS" every time they mention it.  In addition one AH-64D training resource explicitly describes a few ways in which the pilot may access a ground-speed readout while taxiing by way of changing to transition mode or referencing GS on the TSD. If the current behaviour of the HUD airspeed readout was correct neither of these techniques would be required.  

The below HDU video (although from an E-model) shows the TAS and GS readouts not being identical below 5kts.

 

If anyone from ED wants the document references drop me a PM.

Edited May 4, 2022 by Scaley
video link added

[BIGNEWY]

I have spoken with our SME's and we will investigate some more

thank you

[BIGNEWY]

reported to the team for improvement

thanks