MDA - When do YOU go around?

[Okavango]

Most training received agrees that the MDA (including PEC in a light twin) is the altitude you must not go below. Reading David Hoy's book it suggests that's the altitude you make the decision and initiate the go around (so presumably descending up to a further 50ft). David Hoy's book states "The precision approach OCH includes an aircraft height loss allowance to allow for the initiation of a missed approach". So if you'd calculated the MDA (including PEC) as 300ft for example - where would you initiate the go around - 350ft or 300ft and if initiated at 300ft in the UK with an assumed undershoot to follow would an IR examiner give an immediate fail? General consensus would be great.

[Officer Kite]

Most training received agrees that the MDA (including PEC in a light twin) is the altitude you must not go below. Reading David Hoy's book it suggests that's the altitude you make the decision and initiate the go around (so presumably descending up to a further 50ft). David Hoy's book states "The precision approach OCH includes an aircraft height loss allowance to allow for the initiation of a missed approach". So if you'd calculated the MDA (including PEC) as 300ft for example - where would you initiate the go around - 350ft or 300ft and if initiated at 300ft in the UK with an assumed undershoot to follow would an IR examiner give an immediate fail? General consensus would be great.

Do not go below MDA under any circumstances. The official tolerance is 0ft below and 50ft above MDA. Your IR examiner will be working on this rule.

[Banana Joe]

At my flight school, they did not add any margin to the MDA so we would execute a CDFA down to the MDA and then go around. They have recently changed this and now they use a Derived Decision Altitude for NPA by adding a 30ft margin (good enough for a light MEP). So it's really up to what the school has as an SOP and you ought to ask your chief instructor or head of training. However, the tolerance is 0ft below the MDA, no dip allowed.

[eckhard]

David Hoy's book states "The precision approach OCH includes an aircraft height loss allowance to allow for the initiation of a missed approach".

An MDA is not applicable to a precision approach, so the quote above is not relevant to your question. The OCH for a precision approach (ILS, MLS, PAR, GLS) is used to calculate a Decision Altitude or Height (DA/H), which as its name suggests is the point at which the decision is made to continue with the approach or to go around, depending on the acquired visual reference. As David Hoy points out, there is an allowance included to cater for the height loss during the go-around.

With the old-fashioned “dive and drive” technique for Non-Precision Approaches, the OCH is used to calculate an MDH/A. The aircraft is flown down to that height/altitude and levelled-off as it continues towards the Missed Approach Point. At the MAPt, the decision is then made. Given that most MAPts are on or close to the runway threshold, it is obvious that this technique is not ideal for high-performance aircraft.

In the “constant-descent final approach” (CDFA) technique for NPAs (which one would hope is now pretty universal), all available aids are used to help construct an approach slope towards the threshold which emulates a precision approach as closely as possible. There is no level segment and the decision to continue or go around is made by reference to the altimeter, as it is on a Precision Approach; however, as the only published limit is an MDH/A, it seems sensible to add 50ft to the MDA to ensure that one does not go below during the go-around manoeuvre.

Some operators (mine included) may have approved procedures which do not require the addition of any allowance but in the case of a single-pilot light twin IR test, it would be prudent to add the 50ft. It might be worth discussing your intentions with the examiner during the briefing, to avoid any costly misunderstanding.

[Okavango]

An MDA is not applicable to a precision approach, so the quote above is not relevant to your question. The OCH for a precision approach (ILS, MLS, PAR, GLS) is used to calculate a Decision Altitude or Height (DA/H), which as its name suggests is the point at which the decision is made to continue with the approach or to go around, depending on the acquired visual reference. As David Hoy points out, there is an allowance included to cater for the height loss during the go-around.

With the old-fashioned “dive and drive” technique for Non-Precision Approaches, the OCH is used to calculate an MDH/A. The aircraft is flown down to that height/altitude and levelled-off as it continues towards the Missed Approach Point. At the MAPt, the decision is then made. Given that most MAPts are on or close to the runway threshold, it is obvious that this technique is not ideal for high-performance aircraft.

In the “constant-descent final approach” (CDFA) technique for NPAs (which one would hope is now pretty universal), all available aids are used to help construct an approach slope towards the threshold which emulates a precision approach as closely as possible. There is no level segment and the decision to continue or go around is made by reference to the altimeter, as it is on a Precision Approach; however, as the only published limit is an MDH/A, it seems sensible to add 50ft to the MDA to ensure that one does not go below during the go-around manoeuvre.

Some operators (mine included) may have approved procedures which do not require the addition of any allowance but in the case of a single-pilot light twin IR test, it would be prudent to add the 50ft. It might be worth discussing your intentions with the examiner during the briefing, to avoid any costly misunderstanding.

All good and sorry for the incorrect terminology, so lets say we have a Decision Altitude of 300ft (including PEC from a published 250ft) - where would you commence the go around procedure - at 300ft or 350ft? My understanding is that if you've told the examiner you have DA of 300ft you must not go below that and therefore would commence the go-around at 350ft.

[Banana Joe]

I think you can disregard PEC for your case...

[Banana Joe]

Keep it simple. Add your margin to the published minima. If it's 250 and you add 50ft you go around at 300ft. The limit you must not bust is 250ft.

[ShyTorque]

The clue is in the words Minimum Descent Altitude. The term "decision" doesn't actually appear anywhere in that phrase.

[B2N2]

Decision height or Decision altitude is where you make the decision.
The airplane carries weight and downward momentum so it’s inevitable that it dips below as you transition to a climb.

MDA - Minimum Descent Altitude = do NOT go any lower.

Yes it’s that easy.

[eckhard]

All good and sorry for the incorrect terminology, so lets say we have a Decision Altitude of 300ft (including PEC from a published 250ft) - where would you commence the go around procedure - at 300ft or 350ft? My understanding is that if you've told the examiner you have DA of 300ft you must not go below that and therefore would commence the go-around at 350ft.

Apologies not necessary but the incorrect terminology can cause confusion and therefore produce the wrong answers to your question.

You still seem to have a bit of a mix-up between Decision Altitude and Minimum Descent Altitude.

Just to clarify:

Decision Altitude is used on a Precision Approach (e.g. ILS) and there is no need to add any buffer, unless your PEC is significant, which is unusual on a modern aircraft. As long as you commence the go-around at DA, the examiner will accept a small dip below the DA, the amount being subjective and dependant on aircraft type. Of course, if you make a handling error and are slow to apply thrust and/or pitch up, resulting in a significant dip below DA, the examiner can still fail you even if you started the manoeuvre at DA

Minimum Descent Altitude is used on a Non-Precision Approach (e.g. NDB or RNAV) and must not be infringed, so if you decide to go around, you must commence the manoeuvre a bit higher than MDA*. An addition of 30 to 50ft is usually enough for a light twin.

So, if you read your recent post again, you can see that if you have a DA of 300ft, you must be on a Precision Approach of some kind* and therefore that altitude is the one where you must start the go-around. You can go below it during the manoeuvre, as long as you initiate it promptly and use the correct technique.

*Unless you have specific approval from your regulator and are carrying out CDFA procedures. Also, some operators are allowed to use the term “DA” for a Non-Precision Approach in these cases. I can see where the confusion arises!

[Okavango]

Thanks all, that makes perfect sense now and was due to slight confusion of terminology which you've cleared up.