Unstick speed low

[kuobin]

Hello gentlemans:
There is a specific detective item on FOQA system named "Unstick speed low"any body knows what is it and how to avoid ?Thanks...:rolleyes:

[TopBunk]

What it is - getting airborne at too low a speed for the conditions.

How to avoid it? - apply rigour in determining the required speeds (cross-checking weights, flap settings, runway data etc) then rotate at the correct rate at that speed.
:confused:

[Old Smokey]

I suspect that the reference is to Vmu - Minimum Unstick speed. Done as part of normal certification flight testing to ascertain the minimum speed at which the aircraft can be forced to 'break ground'. It's a part of the [rocess of deriving Vr.

Some pretty impressive testing videos from Boeing's flight tests if you can get them, the aircraft with a lump of wood attached to the rear under-fuselage for the inevitable (deliberate?) tail strike, the wood being in abundant supply from the forest just across the road from Boeing.

Regards,

Old Smokey

[Mad (Flt) Scientist]

It's deliberate in most if not all cases ...
10. TAKEOFF AND TAKEOFF SPEEDS - §§ 25.105 AND 25.107 (PART 25 AS AMENDED THROUGH AMENDMENT 25-42).
(5) Section 25.107(d) - Minimum Unstick Speed (VMU).
(viii) VMU Testing for Geometry Limited Airplanes.

(B) The criteria for demonstrating the capability for a clean liftoff and fly-away are as follows:

(1) The airplane’s pitch attitude from a speed of 96 percent of the actual liftoff speed must be within 5 percent (in degrees) of the tail-dragging attitude to the point of liftoff.

(2) During the above speed range (96 to 100 percent of the actual liftoff peed), the aft under-surface of the airplane must have achieved actual runway contact. It has been found acceptable in tests for contact to exist approximately 50 percent of the time that the airplane is in this speed
range.

[ITCZ]

Kuobin asked There is a specific detective item on FOQA system named "Unstick speed low"any body knows what is it and how to avoid ?
TopBunk replied How to avoid it? - apply rigour in determining the required speeds (cross-checking weights, flap settings, runway data etc) then rotate at the correct rate at that speed.
As someone involved in FOQA, I liked TopBunk's reply.

There is a tendency for some to take a look at FOQA parameters and then work out a strategy for avoidance. That is doing things backwards.

The important thing to understand about FOQA is that the QA part is - Quality Assurance.

QA seeks to determine if the techniques, skills, training and SOP used in your operation are working for you.

Your operation should be hiring pilots with good basic skills, it should be training them in the correct knowledge and procedures to safely operate its aircraft.

In FOQA, a flight operations department it scrutinizing itself at least as much as it is scrutinizing individual pilot actions. A FOQA program identifies not only intentional violations of SOP (rare) but more often identifies weaknesses in SOP, training deficiences, etc.

When you first look at FOQA parameters, you see a set of hard and soft limits. It is easy to then think "I must avoid this." But that misses the point.

The example I like to use is that of a beginner golfer.

An ab initio golfer might think as he lines up his shot..
"I better not hit the ground before the ball"
"I better not hit the ball into those trees"
"I better not go too far in my backswing"
"I better not move my head as I swing down"
"I better not hit it too softly, it will go in the lake"

This golfer is thinking in terms of avoiding negative consequences.

Far better if our new golfer gets some lessons and gets a good basic technique and then thinks as he lines up his shot..
"Hmm, 150 metres, light wind from the left, uphill lie."
"I will use a 5 iron, aim for that point just left of the flag, and use an easy full swing.."

This golfer is thinking about a goal, making a decision before playing the shot, and employing sound technique.

I'd say the second golfer will have better success and enjoy his game more than the first.

The second golfer may use a teacher or a video camera to review his technique and make improvements. That is QA.

Bringing this back to piloting, our pilot should not be thinking of Vmu. Our pilot should have an accurately calculated set of V speeds. VR will be above Vmu.

At VR he will smoothly rotate the aircraft at the recommended pitch rate (4 degrees/second in my airplane) to the target climb attitude.

Power + Attitude = Performance

In place of the golfer's teacher or videocamera, the FDR will be recording away happily. When downloaded, the FOQA analysis will compare the flight phase with the actual performance, and it will worry about things like Vmu, early rotation, late rotation, pitch rate low, pitch rate fast, lift off angle exceeded, climb speed exceeded, climb speed low, etc.....

Leave that to the computers.

We are pilots. Power + Attitude = Performance. Use the correct technique and FOQA will take care of itself.
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