Some clarity required on Decision Altitudes

[Windy Pants]

Chaps/Chapesses,

What is your take on DAs

I have been trained to wait until DA(+Pressure Error Correction) before looking up and following the routine of "DA, nothing seen, going around"

Example DA 560ft PE of 20ft, DA to look up @ 580ft...

So it goes like this "600ft, 590ft, 580ft, DA, looking up, nothing seen, going around"

In the time it takes to perform that, you may drop 40ft, so down to 540ft say before the AC levels and the go around comes about.

With the above situation would you normally fail your precision approach on an IRT, as that situation resulted in me failing my precision approach on my IRT, I'm a bit frustrated as that was how we were taught to do it!

Any views reccomendations for my resit appreciated.

Windy

[Turkeyslapper]

Isn't the DA exactly that....descision altitude (not a minimum descent altitude), so naturally the aircraft may descend slightly through that height as you make the 'D' to and then execute the missed approach?

I have done this on all of my IRTs and it certainly hasn't resulted in a fail...descending below an MDA on a NPA is a different kettle of fish though.

Turkey

[Epiphany]

DA has a zero tolerance in one direction only. If you want to pass an IRT then make your decision before you get there and make sure that you do not descend below it. No IRE can fail you for that but they can all fail you for descending below it.

[Turkeyslapper]

Haven't read the regs recently (perhaps I had better) but from a practical perspective what does a heavy jet do on a CAT 1 ILS....do they commence a missed approach 200 odd feet above the DA just in case they don't get visual at the DA?(I am not a heavy jet driver so I don't know).

Cheers

Turkey

[the beater]

Add 50' for single-pilot ops. Do not go below DA! Remember that the IRE cannot fail you if you are within tolerance, so get to within tolerance and then go around.:ok:

[[email protected]]

Don't agree I'm afraid. MDA is a minimum which you must not go below on a non-precision approach.

DA is exactly that, a decision altitude where you make your decision, if you go below it commencing your go-around that should not be a fail.

[tomotomp]

:ok: afraid i agree with crab :ok::ok:

[Droopystop]

I believe that you must decide and initiate a go around by DA, but there it is accepted that downward momentum will carry the aircraft below DA before the effect of raising lever and/or nose has caused a positive rate of climb. In other words you have to initiate (ie moved the controls) at or before DA. But the best thing is to ask you instructor who will know the policy of the examiner.

[the beater]

Yeah, OK, I accept the above points, but the poster originally mentioned that this was a precision approach. Bit of a mix-up between MDA and DA.

[Wizzard]

Decision Altitude is the altitude at which the decision is made and it is acceptable for the aicraft to descend below this altitude during the go-around manoeuvre. Each class of aircraft has a different DA based on weight which accounts for the "dip" below the DA; helicopters are Class A along with light fixed wing aircraft.

As an aside, during a LPC or OPC the decision may be made up to 50' above the actual DA, something which I have seen used to good avail by many pilots over the years!

[ec135driver]

CRAB (and others) has it right, spoke to a CAA TI recently on the subject

1. MDA - tolerance is +50' -0'
2. DA - go around must be initiated by, tolerance +50' (useful if you are getting a bit ragged at the bottom on a proficiency check!) and -0', in other words the DECISION to go around must be made NOT BELOW the DA. As this nearly always coincides with an (in)voluntary pull with the left hand its not a problem! If you get to DA, then look up, then say "nothing seen".......you will have passed below DA and the decision has not yet been made so....:uhoh:

He mentioned that big jets with a DH of 100' above the runway may actually touch the runway during the go-around!:eek:

As always practicalities rule and if you want to be sure of passing a check, use the +50' tolerance, you cannot be failed for that.:ok:

[JimL]

Best not to reinvent the wheel - go to the relevent guidance; in this case the FAA provide the more concise guidance.

From FAA Notice N 8000-340:

From an operational viewpoint, DA(H) is the limit to which a pilot can descend before having to decide to continue the approach by visual means. If the visual references required to safely continue the approach have not been established before passing DA(H), a missed approach must be executed at DA(H). This does not mean that a pilot waits until arriving at DA(H) before deciding to go-around or to continue the approach based on visual references. The decision making process begins when the approach is initiated and continues throughout the approach. A pilot must continually evaluate course and glidepath displacement information throughout the approach. Knowing that significant changes cannot occur instantaneously, a pilot begins to formulate a decision concerning the probable success of the approach long before reaching DA(H). Although DA(H) is a specified point in space at which a pilot must make an operational decision, the pilot accumulates the information required to make that decision throughout the approach. It is incorrect to assume that all aspects of the decision making process are delayed until the critical instant the aircraft arrives at DA(H). The visual cues, which become available during the descent to DA(H) enhances the pilot’s formulation of the decision, which must be made at DA(H). The operational decision to continue the approach by visual means, however, must be made before passing DA(H). At DA(H), a decision to continue the approach by reference to visual cues is appropriate if a pilot is satisfied that the total pattern of the visual cues provides sufficient guidance and the aircraft is in a position and tracking so as to remain within a position from which a safe landing can be made. However, if a pilot is not satisfied that all of these conditions exist, a missed approach must be executed.

The decision that the pilot must make before passing DA(H) is not a commitment to land. It is a decision to continue the approach based on visual cues. This distinction is important since the possibility exists that, after passing DA(H), visual cues may become inadequate to safely complete the landing, or the aircraft may deviate from the flightpath to a point where a safe landing cannot be assured. Since many variables are involved, the final decision to commit to a landing is the PIC’s and is primarily a judgment based on all the relevant operational factors. The PIC shall usually delay the decision to commit to a landing until the final stages of flare and landing.

(1) The following is a list of statements that describe what DA(H) is:

• DA(H) is a specified decision point.

• DA(H) is the point at which a specific action must be initiated (either continue the approach by reference to visual aids or go-around).

• DA(H) is the lowest permissible height to which an approach with vertical guidance can be continued by reference to flight instruments alone.

• DA(H) is the limit to which a pilot can descend before having to decide to continue the approach using external visual references.

(2) The following is a list of statements that describe what DA (H) is not:

• DA (H) is not a point where a decision or commitment to land is made.

• DA (H) is not a point where the decision-making process begins.

• DA (H) is not the latest point at which a go-around could or should be made.

• DA (H) is not a point where all aspects of the decision are instantaneously formulated.
In a monitored approach (for a two crew operation) the landing pilot, who is the monitoring pilot - i.e. NHP for the instrument part of the approach - makes the decision. As the aircraft approaches the decision point, the HP will call 'decide'; in the absence of a response from the landing pilot, the HP will initiate a go-around. In airlines, the landing pilot (monitoring pilot) is usually the PIC - this makes for better decision making (for obvious reasons).

In a single pilot approach, the auto-pilot acts as the HP and the landing pilot makes the decision to land or go-around; that is why there is (usually) an add-on of 50ft to the DA(H).

All aircraft will 'mush through' the DA(H) with a last second decision to go-around; this is accounted for in the calculations of DA(H). The approach ban was introduced to avoid such situations.

Jim

[jeffham]

In a monitored approach (for a two crew operation) the landing pilot, who is the monitoring pilot - i.e. NHP for the instrument part of the approach - makes the decision. As the aircraft approaches the decision point, the HP will call 'decide'; in the absence of a response from the landing pilot, the HP will initiate a go-around. In airlines, the landing pilot (monitoring pilot) is usually the PIC - this makes for better decision making (for obvious reasons).I have done this when I flew for TWA. I can tell you on a CAT III approach, you "may" touchdown on a go around at 50'. BTW...IMO, the monitored approach is THE safest low visibility approach method in a two person crew. For us, as a First Officer flying the aircraft, if you didn't hear "I've got it" or "approach lights" you commenced the go around at DA in a monitored approach.

[Epiphany]

The theory is fine but Windy failed his IRT by descending below DA. I still think that not descending below the DA in a helicopter is the way to pass an IRT.

In a non-test situation in marginal conditions I would wait until DA but with an IRE watching my LPC I will be calling 'decide' about 30 feet above DA.

[Windy Pants]

I think it's one to put down as a lesson learnt, if you've got +50ft to use then use it, and keep clear of your minimums, then no one can complain! It's just an expensive lesson at £3000 per test, and damn frustrating!

[the beater]

From my copy of FLIGHT EXAMINER (HELICOPTERS) HANDBOOK

Tolerances for starting go-around at decision alt/ht are: +50ft/-0ft,
(SE +100ft/-0ft)
Remember that this is a TEST! What you (and I) do in real life is not relevant here.
Add 50', get within tolerance and then go-around!
You might not agree, but at least you will pass.

[Kalif]

Crab and Tomo and 100% correct in that you make the decision at DA, +50' -0'.

If an IRE failed a pilot for going below the DA, when having made the decision by,or at DA, then the IRE is most certainly incorrect in failing the pilot.

[Non-PC Plod]

Windy,

Assuming it didnt take you 10 secs to say "DA, looking up, nothing seen, going around" and then pull the collective (which would have left any examiner unimpressed), I think we could say he/she was being a bit picky. Unfortunately CAA examiners are the most demanding I have come across. I have seen European and FAA examiners who are like Father Christmas in comparison. Having acted as copilot for people taking multi-crew check rides with FAA examiners, I have been absolutely certain that the result was a fail, (the test having taken 3 1/2 hours, because they kept screwing up the approaches!) yet seen the examiner shake their hand and congratulate them at the end!

[grumpytroll]

Once a helicopter pilot, then an airline pilot and now a helicopter pilot. In a DC-9 on an ILS approach you continue at 700 fpm rate of descent(average based on usual approach speeds) until reaching DA, then make your decision. There is no way you will stop your descent at the DA, ever. You will pass through it coming down and going back up, if you miss. You do not level off prior to the DA or you will lose the glideslope. When you are only 200 feet above the ground, (100 for CAT II) the slightest attempt to level off will throw you off the slope full deflection very quickly. If that happens during any phase of the approach you should go missed. The rule is the same for any aircraft. Now, in a helicopter doing 70 KIAS instead of 140 KIAS you should make your decision and pass through the DA more quickly coming down and going up, but in either case you should never stop at the DA. If you do then you have not performed an ILS approach correctly. The MDA is totally different and the requirements should never be confused in any way with the DA. One is an altitude that is the absolute minimum until reaching the MAP the other is only a point in space where a decision must be made. Cheers

[InTgreen]

Anyone else here nervous with the attitude of "if I were doing it for real, then I'd do it differently"? Surely one should practice their IMC flying skills to the minimums so that you have the ability to fly safely to those limits when you HAVE to. Remembering of course that most people practise IF in good weather under the hood, not in the turbulent uncomfortable conditions that generally go hand in hand with an IF approach to minimums...

Oh and for the record, I agree with Crab as well........:ok:

[Paul Chocks]

As a military pilot (UK), I had always been told to make the decision at DH and that a subsequent dip during the go around was acceptable (and indeed expected, due to momentum). Looking at the ANO, Section 1 Part 5, para 47, it states that:

An aircraft to which this article applies, when making a descent to an aerodrome, shall not:
(a) continue an approach to landing at any aerodrome by flying below the relevant specified decision height; or
(b) descend below the relevant specified minimum descent height;
unless in either case from such height the specified visual reference for landing is established and is maintained.

(a) could be interpreted by some as you must not descend below DH period.

Personally, I think the part "continue the approach" means that as long as you have applied power for the missed approach at or before DH then you're OK.

However, its a bit of a shocker to find your understanding of a rule differs from the IRE's during a test (particularly if its a self-funded initial IR!!) - I feel for you.

[Droopystop]

Wizzard,

Are helicopters cat A? I thought it was based on speeds during inital, final approaches, speed over the threshold and go around.

[the beater]

Paul Chocks says:
Personally, I think the part "continue the approach" means that as long as you have applied power for the missed approach at or before DH then you're OK.
Agreed, that's what you need to do to pass the test. Of course if you do this right at the DA, then you will dip below. This is permissible and would not result in a test fail.
InTgreen writes:
Anyone else here nervous with the attitude of "if I were doing it for real, then I'd do it differently"?

Why are you nervous? We're not talking about 'practicing' here, we're talking about passing a test. In real life, if the weather is such that I have to fly down to DA, of course I'll do it. But on a test why not use the tolerance that you are given to your advantage? You can then practice flying to DA as much as you like. It'll be cheaper than 'practicing' with an examiner on board.
I'd be more concerned with Non-pc Plod's revelation that some examiners will allow pilots to keep practicing their approaches until they get one right!
Flight tolerances during a test are something that are standardised for the general guidance of the examiner. The important point to note is that it refers (in this case) to 'Starting go-around at DA/DH'. Not to 'making the decision whilst continuing the approach'.

The ANO states (thanks Paul Chocks):
An aircraft to which this article applies, when making a descent to an aerodrome, shall not:
(a) continue an approach to landing at any aerodrome by flying below the relevant specified decision height.

A decision as to whether to pass or fail a candidate isn't based on a show of hands on an internet forum, it's based on an examiner assessing as to whether the candidate flew within the tolerances laid down, with an allowance made for weather and other relevant factors.
The candidate in this instance has been told clearly the reason for their fail. They could take a copy of this thread to show the examiner (please Sir, Crab says) before doing it exactly the same.
And failing.
Again.
Or do something radical.
Use the tolerances to their advantage.
And pass.
Come on, Windy, what's it gonna be?

[Kalif]

Hey beater, why the uncalled for reply to Windy?

"The candidate in this instance has been told clearly the reason for their fail. They could take a copy of this thread to show the examiner (please Sir, Crab says) before doing it exactly the same.
And failing.
Again.
Or do something radical.
Use the tolerances to their advantage.
And pass.
Come on, Windy, what's it gonna be?"

Windy stated at the start of this thread that he was failed for going below his DA.
A pilot can quite correctly fly to DA, make the decision to go around, after which the aircraft goes below the selected DA.
It's not a case of "please Sir, Crab says", it's a case of what is laid down, in particular Standards Doc 28.
As others have said, you are allowed to descend below DA / DH.
Just because someone is an IRE or IRRE it doesn't make them correct in all cases, and if what Windy says in his original post occurred then the reason to fail the candidate is wrong and/or a misunderstanding on the part of the examiner.
:=

[AnFI]

Windy:: " So it goes like this "600ft, 590ft, 580ft, DA, looking up, nothing seen, going around" "

DA was (for him) 580ft - in his own words his Decision was AFTER DA - not allowed - not correct - therefore fail - no argument!

"DA," - 1 second
"looking up," - 1 second
"nothing seen," - 1 second
"going around" - decision made (just prior to statement) 3 seconds late!

3 seconds at 8 feet per second = 24 feet late!

..... good educational post though - thank you to Windy - sorry:{:(

[ec135driver]

Much as I sympathise with the idea that you must train and test to do exactly what you would do in real life, it is not possible, especially in SPIFR helicopters.

In testing (for the IRT or OPC/LPC) you have to have a point against which you can assess the candidate, but that point has to have a tolerance, hence the DA +50', -0' Standards Document 28 is not a training document, it is essentially a list of markers against which to assess a candidates proficiency.

In testing the candidate is in a FSTD, in which case he "knows" he will never see the ground unless the examiner has set the WX incorrectly! Or, he is in a helicopter with some form of artificial "blind flying" system, screens or glasses/hood etc. As an examiner you must see that he can fly an approach and knows the limits to which he can operate the helicopter, theoretically and practically.

In real life you are going to have the aircraft setup to fly the approach and be able to take in peripheral cues as they arrive, a flash of the surface in the chin bubble etc and when you see these cues you are going to be flicking your eyes back and fore between the instruments and the outside world until as you arrive at DA you more or less already know what is likely to happen. If you have seen only grey, soft cloud type stuff, you will be going around. If the flashes of surface have become longer and more distinct, you are looking to get those required visual references at DA that will allow you to continue the approach. Remember this is SPIFR, the pilot has to do everything and that includes looking out! So unless the chin bubble is clear of cloud but the cabin still in it, you are likely to be in a good position to make a sensible decision.

A word on what to do and say at DA when being tested, dont bother with "Decision, looking up, nothing seen, going around" - JUST DO IT! If you initiate the go-around at (or within +50') the examiner will pass you. If you initiate the go-around below DA (-0') because you talked for 3 seconds, he will fail you. You only have to tell ATC when you are going around, because they cannot tell when you pull pitch, the examiner can!

[TeeS]

Hi JimL
The FAA document may be the most concise guidance and I have to say it sounds sensible, however it is not really applicable for passing a test with a UK examiner. As 135 driver rightly says, the guidance to examiners in the UK is found in 'Standards Document 28' which states:

21.2 The candidate need not be failed if a height error of >100 feet occurs two or three times, but should be failed if any of the following occur:

Height error >200ft;
Height error >100ft sustained (& uncorrected) for an unreasonable time (normally about 15 secs);
At DH/DA, if the candidate fails to initiate the go around within 50ft of the DH/DA; or
If the candidate fails to maintain the helicopter within +50ft of the MDH/MDA at the MAPt.



Note, the requirement to initiate the go around is the CAA's bold, not mine. Doc 28 can be found here. (http://www.caa.co.uk/docs/33/Stds%20Doc%2028%20V2.pdf)

Regards

TeeS

Sorry JimL, I wasn't trying to teach you to suck eggs, the quote and link were for the benefit of Windy.

[wde]

From the Transport Canada Flight Test Guide (Helicopters) TP 14728E (11/2007)

Precision Instrument Approach (3D) Performance Criteria

Base the assessment on the candidate’s ability to:

a. select and comply with the ILS instrument approach procedure to be performed;
b. establish two-way communications with ATC using the proper communications phraseology and
techniques, either personally, or, if appropriate, directs co-pilot/safety pilot to do so, as required for the phase of flight or approach segment;
c. comply in a timely manner, with all clearances, instructions, and procedures issued by ATC and
advise accordingly if unable to comply;
d. select, tune, identify and confirm the operational status of ground and aircraft navigation equipment to be used for the approach procedure;
e. establish the appropriate aircraft configuration and airspeed/V-speed considering turbulence, wind shear, microburst conditions, or other meteorological and operating conditions;
f. complete the aircraft check list items appropriate to the phase of flight or approach segment, including engine out approach and landing checklist, as appropriate;
g. apply altitude corrections to all minimum altitudes depicted on the approach chart used when aerodrome temperatures are 0 degrees Celsius or colder in accordance with the General Section of the Canada Air Pilot;
h. prior to final approach course, maintain declared or assigned altitudes within ±100 feet without descending below applicable minimum altitudes and maintain headings within ±10 degrees;
i. apply necessary adjustment to the published Decision Height (DH) and visibility criteria for the helicopter approach category when required, such as NOTAMS, inoperative helicopter and ground navigation equipment, inoperative visual aids associated with the landing environment;
j. on final approach course, allow no more than ½ scale deflection of the localizer and/or glideslope indications;
k. maintain declared approach airspeeds within +10/-5 knots;
l. maintain a stabilized descent to the Decision Height (DH) to permit completion of the visual portion of the approach and landing with minimal manoeuvring; and
m. initiate the missed approach procedure, upon reaching the DH, when the required visual references for the intended runway are not obtained.

Nice fuzzy language to allow the examiner some latitude in determining if the pilot was aware of what was going on with the approach.

W

[Epiphany]

I suppose if you are taking a test the time to find the answer is after the examiner briefs you and ask 'Any Questions?'

[Wizzard]

Wizzard,

Are helicopters cat A?

Yes, they are:)

[Droopystop]

Wizzard,

Could you elaborate, the only reference I can find shows that helicopters are typical of Cat A (ICAO). The reason I ask is that if you are doing 150kts on initial approach, the course reversal procedure for Cat A + B might be too tight in certain wind conditions. I accept that one can always be doing less than 100kts at the threshold making the last bit cat A, but my understanding is that your cat depends on your speeds at all points of the approach and go around.

[212man]

Doc 8168 Pt 1 explains the Category criteria well and they are purely a function of speed at the threshold, although the other segments will assume different speeds. The maximum speed for a course reversal for a Cat A procedure is 110 kts, however normally the procedure would be Cat A/B so the design would accommodate 140 kts - the Cat B speed. If you want to fly faster than that you'd need to follow the Cat C procedures (which are typically what you'll find in your FMS.)

Additionally, it states:

6.1.3 The missed approach should be initiated not lower than the decision altitude/height (DA/H) in precision approach procedures

This clearly indicates that initiating the missed approach below the DA will run the risk of infringing the protection afforded in the procedure design.