AF447 Thread No. 3

[OK465]

Here's another example of wind effect on AOA at a given FPA for HN 39 & TST.

You're flying an ILS in no wind. You've established the proper pitch attitude and power setting at the proper IAS (resulting in the proper AOA) to maintain a 3 degree FPA (Glide slope) on the facility fixed beam which is independent of wind.

A headwind component develops. You have two options to maintain an absolute 3 degree FPA.

Option #1. You can increase power and pitch attitude while maintaining the same IAS (& same aero AOA, but increased inertial AOA by the amount of the pitch increase) resulting in a lower descent rate at the lower Gnd Spd to maintain the 3 degree FPA. This is what is normally done.

or Option #2. You can hold pitch attitude constant and increase IAS with thrust (& consequently TAS & Gnd Spd) which decreases the effective aero AOA, keeping the inertial AOA constant, while maintaining the 3 degree FPA.

Thrust level sets a rate of 'potential energy' decay which takes you from altitude XXXX to the runway surface at a constant 'kinetic energy' level in a controlled set of conditions. Kinetic energy is then reduced on the runway by thrust reversing, brakes, drag chute, arresting gear, etc.

Just the reverse holds in a tailwind conceptually.

(BTW TST, what's getting sensed CAS-wise at 60 AOA may put the sensed TAS somewhere between 89 & 151 knots, I don't know)