High Altitude Operations & Airspeed
Posted by squawk1018@reddit | flying | View on Reddit | 17 comments
I want to make sure my understanding of high altitude operations and airspeed are correct:
For example, an Airbus A320 takes off and climbs at 250 KIAS until 10,000 feet. The true airspeed increases (roughly 2% per 1,000 feet in a standard atmosphere) due to the aircraft flying at a lower AOA to fly faster through the air to maintain the selected 250 KIAS. At 10,000 feet, the Airbus accelerates to 310 KIAS. True airspeed accelerates accordingly (60 knots). As the aircraft continues climbing, true airspeed continues to increase while indicated airspeed remains the same. Beyond a certain point, as altitude increases, indicated airspeed begins to drop due to very low air density in the upper atmosphere. Although the indicated airspeed is dropping, it is still reading a much higher reading than it would at sea level at the same true airspeed due to the compressibility error (aircraft is traveling so fast that molecules don’t move out of the way in time). Meanwhile, TAS and Mach number are still increasing as the aircraft takes advantage of a lower density atmosphere to fly faster. The ADC uses a formula to calculate the appropriate IAS needed to fly based on coffin corner parameters and cost index.
Should pilots know this formula and how the ADC calculates the appropriate IAS based on OAT, aircraft weight, air density/temperature, etc?
Bot_Marvin@reddit
Bro I just press flight level change
Difficult-Put9586@reddit
ICETea is a Pretty Cool Drink
Indicated corrected for Position error = Calibrated Airspeed Calibrated corrected for Compressibilty error = Equivalent Airspeed Equivalent corrected for Density error = True Airspeed
This is all you will need to know for the exam.
After the exam, just fly what the POH or the SOPs say.
zck-watson@reddit
Sir this is a Wendy's
saml01@reddit
Mach number is increasing because the speed of sound at higher altitude is decreasing.
Sugar_Cane_320@reddit
I’m here to tell time, not build the clock.
saml01@reddit
But according to the FAA youre supposed to know how every piece of it works.
diegom07@reddit
ADIRU does the computing I just fly whatever the OFP tells me to
T0gaLOCK@reddit
Idk what I just read.... I am a CA in the 320. I just take off, pull 300 and switch to .79 and call it good.
Prestigious-Way-710@reddit
As others have said with one slight difference…in the 10 we would clean up which (if we were making money) would take about 270 kias to get the slats in…so we were at 270 kias as soon as possible (well below 10,000 msl) At 10,000 accelerate to our climb speed in kias for our gross weight, at where our climb kias Mach climb crossover hit Mach hold (about FL 240) and head on up to our cruise altitude. More button pushing in the steam era. We just flew it the way the company and the maker said to fly it.
I processed flight test data at Edwards. I became a pilot to avoid that crap and offices.
Trick-Ad-4550@reddit
Indicated airspeed really doesn't mean anything at the higher altitudes (Above ~28,000 ft). That's why we use Mach.
Charlie3PO@reddit
Overall decent understanding, a little nitpick though. While climbing up to 10,000ft at constant IAS/CAS (assuming IAS and CAS are the same, for simplicity), the AOA will remain essentially the same. Lift is related to AOA and IAS/CAS, not TAS. If IAS/CAS stays constant, so does AOA for constant lift, for low Mach anyway. Once you get to a higher Mach number, the relationship starts to warp, but below 10,000ft at 250kts you're not at high Mach.
To answer your question though, you don't need to know how an ADC calculates your limitations. That's very much the domain of aeronautical engineers.
Necessary_Topic_1656@reddit
The airspeed at 10000 depends on the CI
It could be anywhere from 270kts at CI0 to 340kts at CI 999
Chemtrailcreator@reddit
Your basic explanation is correct, however we don’t necessarily climb at 310 knots, it could be faster or it could be slower just depending on what cost index we are flying. The box figures out a speed schedule based on the cost index number, temperature, and a few other atmospheric conditions.
Designer_Buy_1650@reddit
Most pilots don’t know the formula. They totally understand the concept, though, and that’s what matters.
yerbderb@reddit
Idk man I just fly the airspeed company tells me to
Mike__O@reddit
Your entire preamble is correct. The answer to your question at the end is no. You push the button and let the computer do all the higher math. If you're hand-flying you keep the speed on the bug and between the feet. Don't ask questions about how those numbers are calculated by the magic box.
rFlyingTower@reddit
This is a copy of the original post body for posterity:
I want to make sure my understanding of high altitude operations and airspeed are correct:
For example, an Airbus A320 takes off and climbs at 250 KIAS until 10,000 feet. The true airspeed increases (roughly 2% per 1,000 feet in a standard atmosphere) due to the aircraft flying at a lower AOA to fly faster through the air to maintain the selected 250 KIAS. At 10,000 feet, the Airbus accelerates to 310 KIAS. True airspeed accelerates accordingly (60 knots). As the aircraft continues climbing, true airspeed continues to increase while indicated airspeed remains the same. Beyond a certain point, as altitude increases, indicated airspeed begins to drop due to very low air density in the upper atmosphere. Although the indicated airspeed is dropping, it is still reading a much higher reading than it would at sea level at the same true airspeed due to the compressibility error (aircraft is traveling so fast that molecules don’t move out of the way in time). Meanwhile, TAS and Mach number are still increasing as the aircraft takes advantage of a lower density atmosphere to fly faster. The ADC uses a formula to calculate the appropriate IAS needed to fly based on coffin corner parameters and cost index.
Should pilots know this formula and how the ADC calculates the appropriate IAS based on OAT, aircraft weight, air density/temperature, etc?
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