Flying faster because of decreasing winds

[Chris Scott]

Excellent one, Mark1234! All correct.

Quote from galaxy flyer:
I don't know if we invented "managed IAS", but the USAF uses something like this on its heavy transports. Originally, it was computed by the flight engineer, using approach TAS adjusted with current tower winds to calculate a "reference GS", the pilots then added enough knots to fly the plane at a groundspeed that was equal to the "reference GS". Later, it was automated thru the FMSs which did the calculated and displayed the "reference GS" and produced an aural warning, if the actual GS was less than reference GS.
It came out of windshear accidents and the ability of INS systems to show real time ground speeds. I thought it was useful for aircraft which have high momentums and low excess power-the C-5, for example. That said, we still had prohibitions about operations in windshear and TRW conditions.
[Unquote]

Thanks for answering my question (in post #5), and I think you have covered about two-thirds of the whole GS-mini subject in just two paragraphs. It confirms my contention that the technique predated the A320. As they say, there is nothing new under the sun.

What you describe, once it had been automated, sounds pretty close to Airbus's "managed" IAS.

You hit the nail on the head when you talk of aircraft that have little surplus power/thrust, like your C-5. Without comparing typical thrust-to-mass ratios on various aircraft, I guess heavy B707s are also underpowered, and presumably B-52s.

B707s were retrofitted with INS eventually, but I don't remember Boeing offering guidance of this kind, which would have been useful. The only "additive" we used to apply to the "bug" (VREF) was a mental one (no objection to that) based on the surface wind (half wind speed + gust, up to a maximum of 20kt). Can't comment on early 747s; but framer tells us that "Qantas boeing crew use RGS or reference ground speed. It basically provides them with a ground speed they don't go below. Works well."

It's only fair to admit that most twins, including BOAC's and SR71's B737, have the luxury of a good thrust-to-mass ratio in the all-engine case. Maybe that is why they can stick to the old version of energy management on the approach: simply chasing an IAS that is based only on VREF, plus an increment for the wind on the surface – which wind may be zero.