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Levkov

Logic behind "airspeed alive" callout

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Taxiing around Prestwick today in 15-20 knot winds, I heard the callout during ground turns 4 or 5 times. Does it sound every time when airspeed indicator moves above certain value regardless of anything else? If my FO did it every time during taxiing in real life, I would probably smack him over the head with the FCOM :D

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Airspeed Alive is called out by the Monitoring Pilot during the take off roll when both airspeed indicators are indicating positive speed , typically at 40 Kts. I would imagine that you were getting it during your taxi because the gusting wind was fooling what ever logic was used to program the virtual first officer in which ever addon you were using.

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The ASI needle on many big aeroplanes won't start showing an indication until perhaps about 40 knots (less on smaller stuff like gliders etc, since they can still be flying at 35 knots, thus they need an instrument sensitive enough to show that). So if there is any sort of automated callout to indicate that the instrument's needle has started moving, an increase in air pressure from the wind would trigger it (perhaps repeatedly, as you witnessed, when the speed fluctuates in a turn where you are going into and out of the wind, i.e. 20 knots groundspeed into a 20 knot headwind would likely make it trigger repeatedly, since it reads airspeed and not groundspeed).

 

It's imporant to make that call on big aeroplanes to confirm the ASI is working well before V1, so you can abort the takeoff if you don't have a working ASI, especially on the Captain's side, because that is usually the one with its data linked to the transponder which transmits your speed to ATC scopes. Such failures can and do occasionally occur, because the pitot heads and static ports can get blocked by many things; birds nesting in them, insects flying down them, or more critically, if the aircraft is washed and the ports have been taped over during that process and the tape has been left on (this has caused several fatal crashes in the past, so it is one of the things you should look for on the walkaround of an airliner, especially if you know it has been washed. International rules now state that any taping of external ports or pitot heads for whatever reason should now be done with high visibility tape which should be able to be seen during a walkaround inspection in the dark, just in case some dumbass leaves it stuck on there). Note that you are supposed to also crosscheck yours and the co-pilot's ASI's are both reading the same when you hit 80 knots (with the '80 knots: crosscheck' call out) as an additional safeguard, because a partially blocked pitot head can still show some movement.

 

On simple GA aeroplanes with a single pitot tube, it's easy to check it before take off on the walkaround (and you should, cos birds love nesting in the various alcoves, nooks and crannies of GA aeroplanes left parked on airfields for extended periods), by having someone look in the cockpit whilst you move the palm of your hand over the hole, which will cause enough of an air pressure change to make the needle move ever so slightly - and never ever blow down it on a real aeroplane to 'test it', you'll probably break it if you do that!

 

Incidentally, the reason the pages in an FCOM are in ring binder format, is so that if you do choose to smack your co-pilot over the head with it, you can remove a suitable amount of pages in order to vary the severity of the blow to their head. :smile:

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Part of this is the way the simulation treats wind..., it modifies IAS..., simple but leads to many problems when trying to do a precise simulation.  There's been mention of maybe using TOGA as a prerequisite for the call out but I doubt they're going to change it.

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The airline I fly does not use an "airspeed alive call" but an "80 kt" call instead. This also serves as a comparison check as well as the point whereby an RTO will only be actioned for a fire, eng fail or unsafe condition, prior to the V1 call.

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I know why the call is there in real life, and it is the default PMDG FO, not an addon program. I just think that perhaps it could be tied to thrust lever position or something similar that would distinguish takeoff from crazy wind.

 

And Alan, I really didn't know that about the FCOM, I always thought the rings were there to remove the pages when maintenance can't be bothered repairing a non essential system, so they just remove the pages referring to it and pretend the item in question never existed :Devil:

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