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Asymmetric go-around decision height in light twins

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Asymmetric go-around decision height in light twins

Old 30th Nov 2014, 11:24
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Asymmetric go-around decision height in light twins

Asymmetric go-around decision heights are not published in any manufacturer's POH. That is because there are too many variables involved. Individual flying instructors may teach a decision height during initial twin endorsement but this is usually because they were taught that height by whoever did their own twin endorsement. Whatever height is nominated is certainly not based on measured flight tests.

This brings into question the validity of a section of the CASA Part 61 Manual of Standards covering operate multi-engine aeroplanes.
AME.6: Manage engine failure and malfunction during approach and landing
Para 2.6 (B) states: Nominate decision height for landing.

Accepting that fact that aircraft manufacturers do not publish a minimum decision height for a single engine go-around in light twin engine aircraft, then requiring a candidate to nominate a decision height during a test when there is no POH figure published, would indicate this should not be an assessable item and the requirement to nominate such a figure is invalid.
............................................................ ............................................................ ............................................................ ...................................

In th past, PPRuNe has seen numerous discussions on pilot technique to be used if a wing should drop at the point of stall. The expression "pick up the wing with rudder" is frequently used in this context and there is little doubt many instructors teach students to skid the wings level before applying aileron. This is of course faulty technique and has the potential to cause an incipient spin in the direction to the dropped wing. Nevertheless the technique is almost universally taught at flying schools.

Having said that, it is interesting to note that Part 61 Manual of Standards at page 131 (Competency standards) paragraph 2.9 TR-SEA.9 - Operate aircraft in flight, states at sub-para (d) - (demonstrate approach to the stall and stall recovery) the following actions:

(I) recognises approaching stall symptoms;
(ii) reduce AOC at the stall;
(iii) prevents further yaw with rudder;
(iv) apply recommended power;
(v) when the wings are unstalled, level them using aileron control;
(vi) recover height loss

This would seem to put the kibosh on the popular teaching for a wing drop at the point of stall, that rudder should be used to pick up a dropped wing to level flight. The operative words are; (iii) prevents further yaw with rudder; In other words only sufficient rudder to prevent the wing from dropping further.
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Old 30th Nov 2014, 11:54
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With regard to the second part of your post, that's the way I was taught and that's the way I have always taught it. It's nice to see someone in CASA has finally decided to put it into print.
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Old 30th Nov 2014, 23:29
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Ditto, Ravan. I learnt over 30 years ago and was not taught to use rudder to force a roll, nor was it a technique during my instructor training in the late '80s. Always was what is stated above: Prevent yaw with rudder, roll after stall recovery.


W.r.t assy decision heights (somewhat tongue in cheek): If the student hits the ground during the missed - it's a fail (nominated too low an asym committal height). If the student attempts to go around instead of landing when below assy commital height but avoided the ground - it's a fail (ignored the commital height 'limitation'). If otherwise - a pass!
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Old 1st Dec 2014, 00:03
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(ignored the commital height 'limitation').

But wasn't that the whole point by the OP? There is no officially published factual data in POH's on so called "committal height". You could come over the fence on one engine 15 knots above the VREF for a flapless and still go around safely. Even with a Seminole a single engine go-around at 200 ft in the normal landing configuration starting with 73 knots, can be done providing the flaps and landing gear are retracted promptly and the nose held down until 88 knots achieved. The problem is here pilots instinctively raise the nose as they apply full throttle on the live engine to the normal two engine climbing attitude like a go-around on two engines.


A single engine go-around commitment height is just fooling yourself. The situation changes second by second depending on airspeed, flap setting. That is why flap selection on one engine on final is best delayed in order to allow more options. But to set in stone (as blindly taught in many flying schools as a matter of policy), a generic committal height on one engine, is not very sensible
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Old 1st Dec 2014, 08:22
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Accepting that fact that aircraft manufacturers do not publish a minimum decision height for a single engine go-around in light twin engine aircraft, then requiring a candidate to nominate a decision height during a test when there is no POH figure published, would indicate this should not be an assessable item and the requirement to nominate such a figure is invalid.
No.

Most AFMs do not publish a minimum height loss for a stall, nor a method of increasing Vref to account for windshear.

Are the corresponding parts of the MOS that require assessment of these things similarly invalid?

You said it yourself:

Asymmetric go-around decision heights are not published in any manufacturer's POH. That is because there are too many variables involved.
It is a matter of pilot technique (company mandated or otherwise) and a good pilot will make a decision based on the circumstances, but not below the committal height. The actual height, as long as it is reasonable, is not important. What is important is that the pilot understands the risks associated with a SE go-around, and mitigates them appropriately. A committal height is just one countermeasure...

I can't believe the person who posted this rubbish:

You could come over the fence on one engine 15 knots above the VREF for a flapless and still go around safely.
and

Even with a Seminole a single engine go-around at 200 ft in the normal landing configuration starting with 73 knots, can be done providing the flaps and landing gear are retracted promptly and the nose held down until 88 knots achieved.
has the gall to question the sensibility of a committal height. Ever wondered why Piper don't produce an accelerate-go chart for a PA44?

If one has the skill to execute a go-around OEI from "over the fence" at Vref +15 with no flap, why would one be 15 knots too fast in the first place?

Teaching a 10 hr newly minted MEACR holder to go-around OEI from 200 FT, or from a fast approach close to the ground is misguided at the least, and criminally insane at worst. Start by reviewing VH CTT at YSBK a while back and go from there....
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Old 1st Dec 2014, 09:14
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I think you are all missing the point. The answer is that an OEI approach should not even commence unless the candidate is assured of getting visual off the approach. That is that the cloud base is well above the MDA or DH. If not stay at cruise altitude, if possible, and divert to the alternate. I won't go into what I think about teaching OEI missed approaches in light GA aircraft. Different story in Transport category aircraft.

Groggy
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Old 1st Dec 2014, 09:46
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Interesting arguments.

A Navajo for example, on an ILS approach, with a minimum of 200 Ft AGL incurs an engine failure in IMC at 300 FT AGL. He arrives at 200 Ft AGL and is not visual...does he go round asymmetric?

Guess he could try, hate to predict the outcome.
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Old 1st Dec 2014, 11:56
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Given the statement below from the PA44 POH, it seems to me that CASA's position is consistent with the overall intent of Piper's advice to pilots:

WARNING

Under some conditions of loading and density altitude a go-around may be impossible, and in any event the sudden application of power during one engine inoperative operation makes control of the airplane more difficult.

ONE ENGINE INOPERATIVE GO-AROUND

NOTE A one engine inoperative go-around should be avoided if at all possible.
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Old 1st Dec 2014, 12:33
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manufacturers do not publish a minimum decision height for a single engine go-around in light twin engine aircraft
They do however publish an OEI rate of climb chart. You know theoretically what the plane can do, you know what CAsA or the terrain requires you to be able to do. Calculate the lowest you can go without infringing the limiting missed approach gradient and you get a minimum decision height for a single engine go-around.
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Old 1st Dec 2014, 14:10
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Teaching a 10 hr newly minted MEACR holder to go-around OEI from 200 FT, or from a fast approach close to the ground is misguided at the least, and criminally insane at worst
The somewhat hysterical outburst above smacks of a tantrum. It has nothing to do with experience level. Either the pilot has been tested and certified as competent by a qualified authority to fly in command on the light twin in question - or he hasn't. He should not be certified to fly in command until he can demonstrate to at least a minimum safe standard the ability to conduct a single engine go-around in the circumstances under discussion.
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Old 1st Dec 2014, 21:00
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Haha. I'm finding this thread very amusing. So many posts here missing the obvious.
NIK320 is the only one that spotted it. You're supposed to work out your own minima if your ac can't meet the climb gradient required on one engine from the charts provided by the manufacturer.
Here is a practical example. We regularly fly into an airport that has an elevation of almost 5,500ft and from the ATIS we get the temp at the field. If the temp is above a set value we increase our minima so we can assure the a/c meets the climb gradient required to clear the surrounding terrain if we go OEI while on the approach.
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Old 2nd Dec 2014, 00:49
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If one has the skill to execute a go-around OEI from "over the fence" at Vref +15 with no flap, why would one be 15 knots too fast in the first place?
Easily happen when teaching students on their initial light twin. Gust factors, ham-fisted flying, you name it. After all, it is common knowledge (and this is from personal experience) to see airline aircraft at the flare 15 knots or more too fast beyond the published VREF.

However, back to the point made by the OP and that is the nomination of one arbitrary or generic 'committal" height during a single engine approach below which the pilot is supposed to, if necessary, commit himself to a forced landing or prang on the runway rather than risk a go-around. 400 feet seems to be a favoured figure used in initial twin training schools. IMC go-arounds from an instrument approach are a different matter altogether and responders are right in that a calculated MDA is a wise move in the pre-planning of the approach.

Instructors have a responsibility to teach their initial twin candidates a realistic altitude on short final below which a single engine go-around becomes a marginal manoeuvre. It is good instructional technique to start off by undertaking single engine go-around training at a safe initial height in a training area. Use 1000 feet above ground level as a simulated airfield level. A series of go-arounds can be practiced at various altitudes, to include demonstrations by the instructor. Repeat until the student is competent. That way, time is not wasted in the circuit area. The same technique should be taught "under the hood" until the student is confident, competent and knowledgeable of all the factors involved.

Last edited by A37575; 2nd Dec 2014 at 01:45.
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Old 2nd Dec 2014, 03:53
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It is good instructional technique to start off by undertaking single engine go-around training at a safe initial height in a training area. Use 1000 feet above ground level as a simulated airfield level. A series of go-arounds can be practiced at various altitudes, to include demonstrations by the instructor. Repeat until the student is competent.
Which is precisely what a certain chain smoking Instructor made me (and others) do in his Seneca 1 all those years ago, when doing CPL and MEIFR training.

But he also had one hard and fast rule re assymetric go arounds; Once you had gear and full flap down, you were committed to land. A go around from that point was forbidden!

Some may disagree.
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Old 2nd Dec 2014, 05:14
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one engine G/A

There are many considerations, including the performance and capability of both plane and pilot.
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Old 2nd Dec 2014, 11:17
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There is no officially published factual data in POH's on so called "committal height"

FAR 23.1585(c)(2) is pertinent to this aspect of the discussion.

There is nothing preventing the OEM from publishing OEI missed approach data although it is not difficult to see why most civil light certifications avoid it. For military certification processes, the OT&E process usually will be expected to address this aspect of operations.
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Old 2nd Dec 2014, 13:10
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Once you had gear and full flap down, you were committed to land. A go around from that point was forbidden!
Couldn't have put it better myself.

I have some great pics. of the remains of a Piper twin, where the hotshot instructor tried to go around with gear and flap out, they didn't come in quick enough (Ha Ha) because he had failed the engine with the only hydraulic pump. Luckily, both instructor and student got out with very minor injuries, but they went though the ridge of an old barn, you could see the aeroplane shape.

Please remember you are mostly flying FAR 23 aircraft, that says it all.

Tootle pip!!
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Old 2nd Dec 2014, 14:04
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Once you had gear and full flap down, you were committed to land. A go around from that point was forbidden!
Forbidden? Says who? Just another typical instructor's personal opinion and there is no shortage of those as we can see in this thread.

Many scenarios can be discussed if one had the time and inclination. A very high final with full flap and gear on one engine would be one example of a good reason to go-around. But that again depends on the length of the runway and surface conditions. In the case of a PA44 Seminole with mechanical flaps the pilot can dump the flaps to up in less than two seconds with no significant loss in lift but a very quick IAS increase. Select gear to up immediately the flaps are up giving more speed increase then raise the nose slightly and climb away at 88 knots. Nothing could be more simple to a competent pilot. Operative word being "competent"

Obviously techniques may vary for different aircraft types which is all the more reason why the generic 400 feet typical flying school teaching is flawed.
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Old 2nd Dec 2014, 21:53
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Perhaps one should review when to put down the gear and selection of landing flap!
As there are not so many ILS's in uncontrolled airspace then checking visually there is somewhere to land is a good practice.

There are many variables of course. (Waiting for the "what if you are 50kts fast" etc etc.)
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Old 3rd Dec 2014, 09:07
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This is why the asymmetric approach and landing should be flown as closely as possible to the normal one. Carrying too much of a margin in height and speed is no use to you if it means you can't land because you are too high and/or too fast.
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Old 3rd Dec 2014, 14:23
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Forbidden? Says who? Just another typical instructor's personal opinion and there is no shortage of those as we can see in this thread.
A37whatever,
It was also the view a mob called Qantas Airways Ltd., as expressed in the "opinion" of Qantas Airways Ltd Operations Manuals, but Hey!!! what would Qantas performance engineers know about operating aircraft.
In fact, in the aircraft used in Qantas cadet pilot training (mostly Aztec) and after a rigorous risk analysis, Qantas went further, and required that, once the gear was down and the flaps out to any setting, even on all engines a landing was required.
The basis of the risk analysis was quite simple, an all engines approach could turn into an engine out approach at any time.
As far as I am concerned, that is the way to go in any light twin that I have flown (or any B707 or 747 on two) and that includes DC-3/C-47, even though all DC-3/C-47 have dual hydraulic pumps.
That is also the point where you should forget "blue line speed" and fly a speed based on a Vref, with suitable but small increments wind condition and gusts.
FAR 23 light twins should be treated for what they are (and how they have been certified), a single engine aircraft, with twice the chance of engine failure, all the "second" engine does is extend the glide.
What amazes me these days is the loss of "aviation knowledge", go back 40 years (when small twins started to arrive), and what I have said above was common and accepted knowledge, there was no "debate" because the performance limitations were obvious fact, NOT "opinion".

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