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## Departures into IMC - takeoff minima

• Carello
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### Carello created the topic: Departures into IMC - takeoff minima

I'm looking at the paragraph below on page 212 of the eText book

The words "at least equal to" (above) seems to imply that the "landing minima" may only be used to calculate the takeoff minima if the aircraft's landing climb performance on one engine matches or exceed the missed approach climb gradient for the procedure - normally 2.5% but can be higher on some procedures.

If the above is correct, the poor one engine climb performance on light aircraft like OZY will most likely require an increase in the MDA/DA, and hence takeoff minima, to achieve obstacle clearance on the missed approach - particularly on departure when the aircraft is at its heaviest.

For the purpose of the exam, do we assume that OZY's engine out climb performance will not be limiting on the MDA/DA and hence the takeoff minima?

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### bobtait replied the topic: Departures into IMC - takeoff minima

Since the exam gives no data on asymmetric climb performance for VH-OZY, there's nothing you can do to to check if the asymmetric case is limiting. The feed-back I've had is that candidates who make the assumption that it is not limiting see no comment in their KDR. There have been cases for some ILS approaches (Canberra) where DA varies according to the missed approach climb gradient but in those cases, the text of the question indicates the asymmetric climb gradient that applies in that circumstance.

• John.Heddles
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### John.Heddles replied the topic: Departures into IMC - takeoff minima

Further to Bob's observations ..

at least equal to indicates a line in the sand ... if conditions are better, that's a bonus. I suggest that you are reading too much into the words.

if the aircraft's landing climb performance on one engine matches or exceed the missed approach climb gradient This is a black hole problem which I gave up arguing with DCA et al years ago. The general CASA Standards philosophy is that there is enough data in the OEM POH for the pilot to adjust the weight to achieve whatever gradient might be the go on the day. If you believe that, I have a bridge to sell you ...

OEI in a light twin, unless the aerodrome is very much terrain benign, presumes that, once you commit to the approach with a low actual .. then you are committing to land if it turns worse than you expected. A better risk management decision probably is to run for cover elsewhere ...

As an anecdote, on my initial issue Class One (today's MECIR) the DCA Examiner, who was a very practical and risk conscious chap, put me into an ILS at a terrain critical aerodrome and, not far from the minimum, announced that the cloud base was now fluctuating at and below the minimum (we had had the obligatory engine failure just prior to the exchange) ...

Simple answer "continue to the minimum and then land" ..

"But what if you are not visual .. what will you do then ?".

Simple answer "continue to and below the minimum and land"

Inevitably, the call at the minimum was "nil sighting".

He eventually let me out from under the hood at about 50-60 ft above the runway and we duly landed. Now, he was aware of my instrument background (I had been a then unusual airline intake chap in that I didn't have a rating and had, at the time of the present test, about four years on F27 and L188 on a Second Class rating) and certification performance expertise. In any event, passed OK so it was a nil problem situation.

If you put yourself intentionally in a light aircraft OEI approach situation, with any likelihood of needing to go to the miss, then your flight management is lacking sorely (unless the bird is on fire and, then, it just isn't your day).

As to 2.5% OEI on the typical twin, do have a look in the OEM POH, if it has much useful data at all .. and check out just how much weight you would have to be under gross to get away with it ....

As to arbitrarily raising the minimum on the fly ... on what basis might you propose to do this ? First, you don't know what obstacles are critical in most cases and, in any case, you WON'T have the data required to construct the likely flightpath to determine a reasonable height increment to keep you nice.

For both the above situations, a significant problem is that you have no idea what the reconfiguration will take. Another anecdote .. years ago, I used to fly a very nice Shrike Commander. Coming back into EN one afternoon, I thought to check this situation .. with the OK for a missed approach, AND THIS WAS AEO, I commenced the miss from over the threshold with climb power only ... took the entire runway at low level to get reconfigured and to a suitable climb away speed. Now, just have a think about what the situation MIGHT be like OEI ... an absolute world of hurt.

What saves us for almost all occasions .. is the fact that we are probably going to be AEO.

For the exam, Bob's answer is the only reasonable expectation that CASA could anticipate, I suggest.

Engineering specialist in aircraft performance and weight control.

• Carello
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### Carello replied the topic: Departures into IMC - takeoff minima

Thanks John

Like yourself I was looking into the practical (real world) application of the cited paragraph - repeated below.

In a real world scenario basing the takeoff minima on the landing minima will most likely cause obstacle clearance problems if a OEI missed approach is required in an aircraft like OZY. As you say "If you put yourself intentionally in a light aircraft OEI approach situation, with any likelihood of needing to go to the miss, then your flight management is lacking sorely ... "

With the above in mind, would you base your takeoff minima on the procedure alternate minima or something else. I recall reading a CAAP/AIP that talked about raising the MDA/DA to ensure obstacle clearance on the OEI missed approach but I don't know how you would do that for the reasons that you outlined.

Thankfully for the purpose of the exam, the answer is simple.

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### bobtait replied the topic: Departures into IMC - takeoff minima

It's a breath of fresh air reading opinions like these. I have often invited classes to consider a OEI missed approach situation. The idea of raising the MDA to compensate for a dismal asymmetric climb performance is sheer madness. Why give yourself less chance of becoming visual when you desperately need it?

As one student commented "might as well crash at the airport where the ambulance can reach you".

• John.Heddles
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### John.Heddles replied the topic: Departures into IMC - takeoff minima

First, one needs to be pragmatic about the smaller CAR3/FAR23 twins ... they should be considered a bigger single split into a bit on each wing .. generally a good situation if you lose one on the cruise but a worry elsewhere. In reality they form a transition sort of aeroplane bridging the gap between the small single and larger multi ... with some of the benefits of the multi .. .but not many. The light twin is more likely to kill the unthinking, inexperienced, inadequately trained pilot far more quickly than the single during a failure situation. Indeed, there have been numerous experienced and highly trained pilots killed over the years by twins during OEI operations ... generally, though, on these occasions the pilot hasn't exercised his/her usually expected thinking capability in advance.

The main problems, engine wise, are that a failure

(a) drops your effective grunt by something like 85-90% ... NOT 50% .. that relates to power and thrust, not performance. Performance generally relates to thrust - drag ... not a good situation unless the deck is stacked your way. What this means, in summary, is that the OEI climb performance at commercial weights is dreadful and may well be non-existent .. ie, the aircraft is going to descend in spite of whatever the pilot might encourage as an alternative.

(b) introduces a big handful of handling problems at lower speeds ... any trained monkey can fly a twin at cruise speeds but getting out of trouble at low speed sorts the knowledgeable and competent from the fools.

If you are at any decent sort of weight and, particularly, hot and high (ie high DA) then the aircraft won't be going any place far away in an OEI takeoff or landing scenario unless the terrain be very benign (read "flat") and the DA not terribly high.

The pilot who confidently (but in ignorance) lifts off at the POH speed and expects to be able to continue if an engine stops making noise shortly thereafter .. is one very overconfident pilot. Even in an airline jet ... under WAT-limited conditions the post failure continued takeoff performance is pretty average, especially on twins. A similar tale applies for the OEI approach and miss.

One of the educational problems relates to the typical GA endorsement and renewal situation ... two up, not much fuel, low altitude (in Australia) .. and the pilot gets to reinforce a very wrong perception of light twin capability and attitude to OEI flying.

On a related tack, I am always horrified at the silly practice of Vmc demonstrations for post initial twin endorsements .. this puts the aircraft into a critical situation where the available performance is greatly reduced below that which might be available at or above the real world blue line for the day.

Another anecdote, if I may. A close colleague, post 1989, found himself needing to venture forth on light twins after a lifetime of military and airline heavies. During the endorsement the instructor indicated that they would have a look at Vmca. My colleague, very judiciously, managed this foolish ambit by restricting his rudder input so that the departure speed was increased by a margin. The instructor was quite perplexed ... "it usually goes much slower than that ! ". Ignorance is bliss, as they say ...

basing the takeoff minima on the landing minima will most likely cause obstacle clearance problems if a OEI missed approach is required in an aircraft like OZY.

If there is much in the way of terrain about .. take it as guaranteed (depending on AUW and DA)

would you base your takeoff minima on the procedure alternate minima or something else

That's an every time reassessment. Horses for courses and no standard approach to the situation. Generally, a failure at low level should be predicated on a forced landing unless the circumstances are very favourable.

Another (actually numerous) anecdote, if I may. On each and every GA instrument renewal, my briefing included something along the lines of "touch anything below xxx ft and I'll close both throttles and land ahead". Strangely, I was never put to the test on this one ... DCA examiners or Industry delegates alike ...

A generic answer is that one should avoid committing to the OEI approach unless the landing is a near guaranteed proposition.

might as well crash at the airport where the ambulance can reach you

.. unless there be a better option ... such as diverting someplace else where CAVOK might reign supreme.

Engineering specialist in aircraft performance and weight control.

• Carello
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### Carello replied the topic: Departures into IMC - takeoff minima

Thanks John

Your closing paragraph (cited below) is what I expected to hear for an IMC departure in a Class B aeroplane operating under the provisions of CAO 20.7.4

"A generic answer is that one should avoid committing to the OEI approach unless the landing is a near guaranteed proposition."

With the above in mind, I would suggest that entering IMC (on departure) at the procedure "alternate minima" does not provide any guarantee of landing from the procedure should a return to the runway be necessary - we cannot assume that cloud and vis will remain static in time and space. Furthermore, should a missed approach be required following an OEI event the provisions of AIP ENR 1.5 p 4.4.4b (see below) cannot be met in an aircraft like OZY.

In summary, under the best conditions, a takeoff minima based on a procedure landing landing minima provides no guarantee of returning to the departure aerodrome if an OEI event occurs in IMC. To my mind the takeoff minima should always be better than the landing minima - how much better will depend on weather and aerodrome environment.

I would be interested to know how a typical GA operations manual ensures compliance with AIP ERN 1.5 4.4

cheers
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• John.Heddles
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### John.Heddles replied the topic: Departures into IMC - takeoff minima

I would suggest that entering IMC (on departure) at the procedure "alternate minima" does not provide any guarantee of landing from the procedure should a return to the runway be necessary

Suggest you avoid getting into any mindset about "guarantees" when it comes to performance .. you have only probabilities dependent on actual versus certification conditions and, most importantly, the certification standards which apply to the particular aircraft .. not to mention performance deterioration with age.

Since Australia threw the baby out with the bathwater some years ago (post-Yates Report) and adopted the foreign NAA standards, the usual range of US light aircraft, which vary in performance standard greatly, provide considerable problems when it comes to matching reality up with the ivory tower requirements put by the Flight Standards folks in operational CAOs and the AIP.

Previously it was far simpler ...DCA (the original antecedent of CASA) put the requirements into the flight manual for the aircraft and the pilot's task was far simpler. Now, it's hard enough for folks with my sort of background to do it in GA .. while the airline types have (or should have) a tech services operations engineering support team behind them .. how the (non-engineer) new CPL out in GA land is supposed to keep his or her nose clean is rather beyond me ...

As to what minima might be suitable for Captain Bloggs on the day (or night) depends on Bloggs, the aircraft, and the location. You should be thinking in terms of working through the risk assessments and management for each and every case. After a while, of course, your routine runways will develop into something of a standardised approach to this risk management process which makes life a little easier.

the provisions of AIP ENR 1.5 p 4.4.4b

In days of olde, the requirements were much simpler. I well recall when this sort of nonsense first started to appear in the operational requirements. Indeed, I entered into vigorous correspondence with the relevant standards folks in Canberra in a vain effort to have it amended to something having a more sensible relationship to certification and pragmatic engineering ... all to no avail, unfortunately.

The work, technically, is easier with heavies as the data is available to do the sums. For the smaller end of the market, though, the typical OEM POH gives you the minimum that the FAA rules mandate and, invariably, is constrained by the OEM's legal advisors ... keep in mind the litigious environment which is the good old USofA.

I'll leave it for Bob to run you through the nitty gritty details in your courses but consider the following snippets for starters ..

(a) 4.4.3.a Just how do you propose to do this ? It doesn't matter if you are visual or in cloud .. the gradients are so minimal that you cannot assess it on the fly .. you must have done the sums beforehand. Now, that introduces another problem .. from where does the pilot in the field get the terrain data ? As an ops engineer, it's a hard enough exercise for me.

(b) 4.4.3.b Likewise ?

(c) 4.4.4.b Now, that's a really good trick ... if you can find the data to figure it out ...

These particular points were the things I went to bat for many years ago .. but the rationale just fell on deaf ears and and was defeated by ideological philosophies. Some of the on-the-phone-discussion responses left me shaking my head .. but that's another story altogether.

I would be interested to know how a typical GA operations manual ensures compliance with AIP ERN 1.5 4.4

Probably the Industry would prefer that you didn't probe too deeply into that mire. I have no idea how the FOIs map what the POH data sets reasonably provide across to what the poor old operator puts up for assessment in his attempts to get his operation up and running and then keep it out of trouble ..........

Engineering specialist in aircraft performance and weight control.

• Carello
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### Carello replied the topic: Departures into IMC - takeoff minima

"(a) 4.4.3.a Just how do you propose to do this ..."
(b) 4.4.3.b Likewise ?
(c) 4.4.4.b Now, that's a really good trick ... if you can find the data to figure it out ...[/i]

From a practical point of view, the only way of complying with AIP ENR 1.5, p 4.4 in an IMC OEI scenario would be to climb to the MSA within the circling area for a return to the same aerodrome and then to LSALT if intending to land at the takeoff alternate.

This will most likely require a reduction to takeoff weight (by off loading payload and/or fuel) to allow for the reduced climb performance in a climbing turn - not ideal I know. That being said, the charter will most likely be cancelled or the pilot would be fired - either way, problem solved.