Asymmetric ILS Approach

[Angle of Attack]

Just curious to different techniques taught on the selection of DA during an asymmetric ILS in a light piston twin. I have been taught that the missed approach be conducted at asymmetric commital height or the DA, whichever is the higher. The question is, if during a particular approach, the DA is higher than asymmetric commital height, is the missed approach conducted just prior to reaching the DA to prevent sinking below it during the go around? Or is it conducted at the DA?

[A and C]

In real terms flying a light twin on one engine is an emergency so once you have a the gear down and a clear lump of tarmac in front of you realy not going to land ?

If the engine failure is real why have you decided to go to an airport that is on the limits ?

When an engine stops you should review you options to find the best place to land , if the best place has WX below limits you may have to fly below them......this is an emergency remember.

[Avenger]

I have to agree with A+c on this one, if the situation was a real failure, however in terms of IR training it is important to remember the spirit of the test i.e the airfield wx is out of limits, hence the go-around.

In theory, the DA(H) is the hieght at which you should make the decision -land or otherwise, not necessarily a "visual height" because of the type of appoach you may be flying.

If by ACA(H) you have not met the criteria to land i.e clear r/w, permission, etc. then you must go-around.
The ACA for a particular airfield, or a/c is designed to allow a safe go-around in the dirty config, followed by a clean up and climb.
Provided you have made taken the actions to go-around, i.e wheel back, pwr, foot etc., it is permissible to sink below your nominated heights.I don't advise last minute decisions at ACA, if your heavy, dirty and in an old tub, it will struggle to go-around at ACA and the last thing through your mind will be your ankles!

[401]

Avenger

For the IR initial on a twin it is part of the test to do an asymetric go around after an ILS followed by a single engined NDB approach.The go around initially is MDH +50 ft.The MDH is shown in the Aerad approach plate for that particular runway.Add 50 ft to this.If this is 200ft for an ILS the go-around would be initiated at a height NOT to go below 250ft.Below 250 is a fail. Once a/c passes 500 QNH the examiner will close one engine to equivalent of idle thrust.You then have to clean it uo as quickly as possible whilst maintaining runway heading.All drills must be then completed.Once trimmed out and straight and level it doesn't fly too badly(C401)but I wouldn't like to do it with full fuel and 6 pax!!The important thing here is not to drop below the 250 ft and to reset the altimeter to QNH on the overshoot.For the NDB approach on one engine the MDH may be 500 QFE and once this is reached the a/c is flown st and level at exactly 500 until runway is seen.If not overshoot but normally examiner takes over and lands a/c.
PHEW!! I'm exhausted thinking about it.
Next renewal due June so I'll have to start practising again soon.

[A and C]

Why fly the app on QFE ,while you are faffing about with re setting the QNH i will be doing some thing important like planning my next move.

[RVR800]

IMHO...

And to answer the original question

You start your lever movements at DA
If you sink transiently below DA during the
GA its still a pass on the IRT

The DA is the point of DECISION not a
point below which you musnt sink

You START to go around when the DECISION
is made

However in the case of an Asymmetric commital Altitude (I use QNH) go around
being lower than DA - (When would this be
the case? - ACA is Threshold Alt+200
for day for night its THR Alt+300? in a light twin)so its possible for this to occur on an ILS then I would start the GA at (not
before) ACA as well but its a difficult
and good question for an IR Instructor

[Avenger]

O Dear O Dear,

Isn't this getting confusing! I assume if you are doing an ILS, this is a PRECISION approach ,hence we could be on the QNH or QFE and talking DA or DH,

If we are doing a NON PRECISION approach, ref to an airfield, not runway, we should be thinking in terms of MDA/MDH.

The initial IRT could throw an assymetric ILS at you and a two engine NDB or VOR, the format is not set in stone and we should be teaching students this.

If the decision at DA/DH or MDA/MDH is go-around, then as our collegue suggests we initiate the actions and if we sink a bit it's still a pass.

If the decision at DA/DH or MDA/MDH is "land" we normally set flaps, regain the slope and land, but must always be aware that at ACA some helpfull person may pull onto the RW so be Prepared to consider the GA at ACA as well.

**** happens in real life!

[Angle of Attack]

Thanks for the posts...interesting, Yes the question is only on Precision ILS approaches with a DA, Non Precision the procedure is fairly well set in stone, dont go below the MDA, whereas the general consensus seems to be that on an ILS the GA be commenced at the DA or ACA whichever is the higher!?
cheers..

[This message has been edited by Angle of Attack (edited 06 December 2000).]

[aerotowman]

The school where I did my IR had an engine out allowance which was to be added to the value of the published DA. This was published in the schools operations manual, and in the case of the seneca was 100 feet.

Go around on precision approaches are INITIATED at DA, and the aircraft WILL sink below this during the go-around. Of course on non precision approaches you don't go below MDA.

As far as QFE goes, why do we continue with such nonsense? Most IR schools these days use QNH for approaches. The last thing you want to be doing on a go around is messing about setting QNH waiting for the examiner to fail the engine.

How about high altitude airports? Think you can set QFE at an airfield 4000 AMSL?