PPRuNe Forums - View Single Post - Airbus groundspeed mini & unstable approaches
Old 12th Jun 2019, 09:10
  #47 (permalink)  
Uplinker
 
Join Date: Nov 1999
Location: UK
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..........I don't care about maintaining a minimum ground speed, this has absolutely nothing to do with maintaining safe flight..................... I have seen some ridiculously high commanded air speeds whilst using managed speed and A/T...........have seen commanded speeds of VLS plus 40 or more. How likely are you to experience, unannounced, 40 knots plus of wind shear which would threaten the aircraft?

On the other hand I and others alike have flown approaches with very strong and blustery crosswinds where g/s mini will add on nothing at all to VAPP.
....comes from the traditional philosophy, which flies bugged airspeed at all times, (and adds a fixed increment to Vapp on a gusty day). This is how it was done for years, but then somebody came up with the minimum groundspeed concept. And when landing onto a runway fixed to the ground (!!!), the speed over the runway is what actually counts.

So, as above, the traditional pilot who does not understand the minimum groundspeed concept will be nervous to see such changes in instantaneously commanded airspeed, (NOTE, Vapp is not changing), because they are used to absolutely nailing their airspeed within +10/-5 kts. Any deviation larger than that is too fast or too slow for them, and their reflex reaction is to take action to contain the airspeed within those limits.

Which is fair enough, BUT minimum groundspeed is a completely different concept. It maintains energy and reacts to head or tailwind gusts, (which may or may not be expected). NOTE: it reacts the opposite way round to the traditional method, and does so to maintain energy. It has been developed, and tested and refined by test pilots. It works.

The example quoted above ‘adds maybe 40kts’. Well, Yes - I HAVE flown approaches with sudden 40kt gusts a few miles out. ‘But it adds nothing for strong and blustery crosswinds’, no, it probably won’t unless they affect the groundspeed.

By pulling speed, one disables G/S mini, which could leave the Airbus in a low energy state.

Last edited by Uplinker; 12th Jun 2019 at 09:30.
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