# Why do you land a fighter jet with AOA Units?

I currently begann learning Falcon BMS and watched some fighter cockpit landings on YT and learned the technique to land a fighter is to use your AOA and not Airspeed like you would do it on a GA Plane or on an Airliner what is the reason for that ? why are you not calculating the Approach Speeds like you would do it on an Airliner with X-Wind and weights etc. ?

Because AOA is the metric that governs all airfoil aerodynamics. And airline pilots also use AOA, indirectly. They determine (calculate) their landing speeds based on their configuration, (flap/slats settings), and gross weight and this is, effectively, calculating what speed to fly to get that same AOA, (that is the highest AOA, sufficiently below the stall AOA to allow safe stall margin). This allows landing at the slowest speed possible without risk of stalling.

The reason this is done for fighters and large aircraft, and not so much for GA aircraft is because the speed that gets you to that best AOA changes due to gross weight, and landing gross weights, (as a percentage of total gross weight), vary significantly more for fighters and large aircraft than they vary for most GA aircraft. So the landing speed for a small cessna does not need to be adjusted so much for the weight of the plane.

In the F-4, for example, the manual had **two ways to determine how to fly on final approach.

1. Calculate and fly by speed:
a. Full Flaps: 140 Kias + 2 kts / 1000 lbs of fuel.
b. Half flaps: 145 Kias + 2 kts / 1000 lbs of fuel.
c. No flaps: 150 Kias + 2 kts / 1000 lbs of fuel.

Or...

1. Just fly "On-Speed" AOA, referencing one of the several AOA Indications.

**Note: numbers in option 1 are from memory... They not be 100% accurate!

• "+ 2 kts / 1000 lbs of fuel" -- Does that mean +2 kts per 1000 lbs of fuel? Commented Nov 10, 2023 at 17:20
• Yes. That's exactly what it means. Commented Nov 11, 2023 at 2:15

Angle of attack is the most convenient metric of the performance of the wing. One can safely assume the wing will for example always stall at the same AoA regardless of weight or speed.

Flying approaches according to AoA will keep the pilot workload to minimum, and removes possibilities of mistakes in calculations.

The pilot can simply monitor the AoA, and keep it in target value while maintaining glide path by adjusting the throttle. No math, tables or mnemonics necessary.

• Some simple math is needed to compute a corresponding airspeed to cross check against AOA to ensure it is correct. Commented Nov 10, 2023 at 15:05
• Also, stall AoA stays the same when in turning flight. If you fly some wild turning pattern to land after having dropped some payload but not all, determining stall speed beforehand for each bit of the turn will be much more difficult than just fly with the AoA scale I would imagine Commented Nov 14, 2023 at 17:31

While I don't disagree with the other answers, another reason is that AoA is more difficult to measure and is only useful for some parts of the flight (not useful in cruise, for example). So, most GA aircraft, and many airliners do not have an AoA sensor or AoA display. It generally involves adding a mechanical wind vane that sticks out into the airstream and is connected to an encoder. This position then has to be displayed to the pilot. It can't ice up, or be too sensitive to debris impact etc. This all adds cost and complexity. It also adds complexity to pilot operations as it involves an additional display for the pilot scan.
Of course, it can be done, but many aircraft instead only display airspeed. Even pitch is not required for VFR operations, but is for IFR. Flight instructors often repeat, "Look outside!" for pitch. Meanwhile, airspeed measurement for aircraft has been around since the Wright Bros

• I would add that newer designs for AOA sensors have mitigated these issues somewhat. The system I have on my plane (from Dynon) involves a pitot probe with two orifices, one oriented normal to the flight path that measures dynamic pressure to determine indicated airspeed, and another oriented 45 degrees down. a small computer is used to determine AOA by comparing the difference in pressure between these two orifices. No moving parts are involved, and the icing issue is resolved as the pitot probe is (can be) heated just like any pitot probe. Commented Nov 11, 2023 at 16:00
• As to the comment about additional pilot work load, although not in common use, there are many options for communicating AOA to the pilot, some of which actually reduce pilot workload. Commented Nov 11, 2023 at 16:07
• Since maintaining AOA at that AOA where your aircraft is safe to fly at on approach is guaranteed to put you at the optimum approach airspeed considering all factors (gross weight, configuration etc.), one option (used in many military aircraft), presents AOA as a generated aural tone which starts out as a low prf pulsing tone at somewhere around L/D max AOA, increases in prf until just below optimum approach AOA, where it changes to a steady tone at optimum AOA, & changes to a high prf high freq stall warning tone near stall. With this system pilots need not look inside the cockpit at all. Commented Nov 11, 2023 at 16:11
• Most if not all airliners younger than a Boeing 767 should have AoA vanes though. Commented Nov 14, 2023 at 17:28

We may anticipate that most fighter planes are not staticly stable.

When an aircraft is staticly stable, airspeed and angle of attack are set by elevator trim. While on a glide path, the aircraft will self adjust it airspeed and maintain its trimmed AoA.

For an aircraft with nuetral (or even negative) static stability, flying a glide path will involve careful monitoring of airspeed and angle of attack.

Flying by airspeed would involve knowing the aircraft weight, allowing a "safe" amount of elevator trim.

Flying by angle of attack allows the plane to drop into its "natural" linear glide path. From here power is added or subtracted to reach the ground aiming point (generally a runway).

In reality "flying by airspeed" (how your scarf ruffles) and flying by AoA go hand in hand. For a given weight, this can actually be established in flight before approaching to land.

The AoA parameter gives the flight computer a level of redundancy to "fly this airspeed at that AoA". But for a staticly unstable fighter, constant pitch adjustments will be required to maintain proper airspeed.

airspeed and angle of attack govern airfoil aerodynamics

Landing speed will be variable (based on weight), there for landing distance will be variable.

A case for longer runways, or good strong arrestor cables.