Hi Bob,

I had a question come up on a cyber exam:
"The indicated airspeed beyond which full or abrupt control deflection is prohibited is -"

In the same exam, I also had:
"The maximum speed at which full or abrupt control movements can be safely made during normal flight is called the -"

I changed my answer in the first question from Va to Vno, because the term 'indicated air speed' seemed to imply that it was a speed indicated on the ASI. Also having had both questions asked almost back-back made me doubt Va would be the same answer for both...

Am I wrong in thinking that an 'indicated air speed' has to be present on an ASI?

Points of interest -

(a) for a specific aeroplane, one needs to run a review of the design rules relevant to the particular certification to find the detailed story. The rules change over the years as technology permits achieving higher airworthiness standards. The simple way to keep oneself nice is to abide by AFM/POH limitations and recommendations as these are in compliance with the Design Standards applicable to the Type.

(b) for a light training aircraft, the limit speeds may be considered to be equal to what is shown on the ASI. Again the AFM/POH will tell you what is appropriate for your particular aircraft.

(c) Va (minimum) is defined in the pitching plane as the speed at which the aircraft will stall while pulling the limit load factor (think g) ... that is to say, at a speed just short of where damage might be expected to occur to the structure while pulling the limit g .. which certainly covers routine manoeuvring. One can think of Va as protecting the ham-fisted pilot by stalling before excessive loads can be applied to the structure. Be aware, though, that the published Va may well be in excess of the minimum permissible value. In this case, you most certainly won't have anything much in the way of protection for the wing structure.

(d) for some aircraft, pitch may not be critical and Va may be limited to a lower speed by rudder considerations, typically.

(e) up to Va, the aircraft should not sustain damage if any ONE control is moved to the limit stop and held there, providing that the OEM selected the minimum permissible value for Va. There is no intention for simultaneous movement of more than one control or oscillatory movement of any control. Either can lead to severe embarrassment.

Looking to your exam questions -

(a) the question is looking for "Va" (or, perhaps, the specific airspeed value of Va if you have that information in the question)

(b) the question is looking for "maximum manoeuvring speed" or "manoeuvring speed".

Va is not marked specifically on the ASI but will be specified in the AFM/POH limitations section .. a reference to "indicated airspeed" should be read as meaning what the needle is pointing to on the airspeed scale of the ASI. Vno is not tied up with full/abrupt control movements.

John, thank you for all this information! I found it very helpful

All part of helping one another, good sir.

You might look at the envelope diagram referred to in FAR 23 .. www.ecfr.gov/graphics/pdfs/ec28se91.001.pdf ..

If you look at Va, it is at the intersection of the stall line (the curve at the LHS of the envelope .. this represents the maximum g you can pull .. any more and the wing stalls whether you like it or not .. hence an automatic protection against ham-fisted would be pilots) and the limit load (the horizontal straight line from point A .. the stall line continues to higher load factors .. so, above Va, you can physically overload the structure in the pitching plane before the wing stalls .. too much and it's all over, red Rover)