DH, DA and MDA

[Alltheway]

Dear All,

I wanted to clarify Boeing's SOP's for setting minimumms

Cat III specifies set DH
ILS - DA
Non-precision - MDA

Can I therefore assume that both Altitudes would be set using Baro and Decision height would in fact be Radio please?

[kenparry]

Yes.

Cat III is always on radio altimeter, but remember it can be zero. (IIIB or IIIC)

Cat I ILS and non-precision are on the barometric altimeter.

Not just Boeing, this is industry-wide.

[gatbusdriver]

DH is set on the ADI control panel for Cat2/Cat3 ops, with Cat1 DA set on the altimeter.

For MDA we set MDA+50' on the altimeter, so that when decision arrives and we GA then we will not descend below MDA.

[Long Haul]

For MDA we set MDA+50' on the altimeter, so that when decision arrives and we GA then we will not descend below MDA.

Others don't, at my airline we set (M)DA.

[Alltheway]

Thanks Ken Parry,

That was my assumption and thanks for verifying.

Just have to find an FO job now and I'm sorted.

[BOAC]

A Cat I can also be flown to DH minima using the radalt if:-

Company OM permits
Cat I RADALT minima are published for the approach. NB The DH will not necessarily be the same as the DH on a normal chart - it must SPECIFY radio altitude.

Long Haul - which authority are you operating under?

[Denti]

Same as Longhaul here, operating under EU-OPS.

[BOAC]

So, are you saying you expect to go below MDA on a g/a?

[The Real Slim Shady]

I'm with BOAC here.

MDA is exactly that: it takes no account of altitude lost in a go around so you have to add at least 50ft to account for the GA.

[411A]

....so you have to add at least 50ft to account for the GA.

You have to do no such thing at our outfit...we dive/drive, not CDA.
Therefore MDA set, period....not this +50 feet nonsense.

[Long Haul]

Long Haul - which authority are you operating under?

EU Ops, for an airline that had it's 90th birthday this year. I suppose that we do go slightly under (M)DA during a go-around, but it's never really bothered me, to be honest.

[BOAC]

Well, assuming that LH and Denti are not winding us up here, what do you both think the 'M' in 'MDA' stands for? Assuming it is the same word that I think it is, what do you understand by that word, and why it is used on a NPA?

[One Outsider]

Well, if you want to land you will have to go below MDA at some point. If that point is the same as where an eventual GA is initiated it is hardly unsafe. Otherwise landing would be a risky business would it not.

[BOAC]

Now I know it's a wind-up

[One Outsider]

Bang your head all you want. On a CDFA the point where you would continue below MDA for landing is the same as where a GA is initiated if not visual.

EU-OPS takes the same view as adding 50' is only required when flying the approach using conventional means.

Adding 50' is a leftover from the days when steam was used.

[BOAC]

So, you too go below MDA when not visual. I'd be interested to know what these 'unconventional' approach techniques are. Obviously things have changed.

[Denti]

To clarify, our SOP is a bit muddled in that respect as we do set MDA/DA as mininum, however if it is an MDA there is a note saying "If using an MDA(H), initiating a missed approach approximately 50 feet above MDA(H) may be necessary to avoid descending below the MDA(H) during the missed approach". However we do not set it and that note will vanish soon in one of the next OM B revisions.

[BOAC]

It begins to sound as if the 'D' in MDA is slowly changing from 'Descent' to 'Decision' which would be fine. Until then, in my book, a Minimum is just that. Has this been promulgated? Has the means of calculating 'M Decision Altitude' been adjusted? It still seems to me that if no margin is added to 'MDA' then terrain separation can easily be degraded. EUOPS (as usual, a la JAROPS) offers NO useful guidance that I can find. 3 UK operators in my flying time have always added 50' for a 737, including BA

I well recall the many ear-bashings in the sim for going a smidge below MDA on a s/engine g/a

Any ATC folk around who can cast a light?

[Kiltie]

I concur with BOAC here. Perhaps we are both about to get red faces but I haven't heard of EU-Ops removing the 50' increment. You may very well be right though so I am keen to get to the bottom of this. One Outsider can you clarify what you mean by flying a non precision approach by "conventional means?" Do you mean by reference to ground based nav aid signals as opposed to some kind of PRNAV approach using the map display? If so this is a new one on me since we add the 50' increment as always to mitigate the "sink below" risk on go-around froma CDA, and we are EU Ops.

411A adding 50 feet is not a "nonsense". It is a recognised technique for CDAs, but I agree not necessary for dive and drive.

I can understand some companies not bugging the 50' increment per se so long as it is qualified with the rule that the go around intervention must take place prior to reaching MDA.

If this is for real then it opens up an important examining difference which I have not experienced yet on my recurrents under EU Ops

[Eddie_Crane]

Originally Posted by BOAC

3 UK operators in my flying time have always added 50' for a 737, including BA

I can confirm that one of those operators, at least in 2008, required that 50ft be added to NPA Decision Altitudes published in the Performance Manuals (as per Part A(1) Manual).

Edited to add: exceptions are "dive and drive" approaches (e.g. JFK Canarsie, etc.) and RNAV Final Approach procs