DA/MDA setting debate
 

Hi everyone, a recent debate in my company has centered around the proper setting for DA. Some argue that it should match the exact value shown on the Jeppesen approach chart, such as '214 ft,' while others believe it should be rounded up to the nearest increment, like '220 ft.' Which approach should be considered the standard? I've reviewed materials from the FAA, ICAO, and Jeppesen but couldn't find any guidance addressing this specific question. Perhaps it's not an issue that requires much attention, but I'd love to hear your thoughts!

If you fly the aircraft when you can set the exact value, set that. If you don't, round it up to the nearest 10.

The DA is published. We set the value on the chart in the FMS. If I could only set whole tens, instead of 214 I would set 220, not 210.

I thought this was going to rehash DA versus MDA on 2D approaches. I'm disappointed.... ; )

DA is published.
MDA is published + a company specified increment.
Circling is published.

Next time someone challenges you on this, gently tell them this true scenario which happened a few years back at my airline:

Published DA is 214ft. They select 220ft because they want to round it up. Minimums call, go around, can't see the required runway elements. They set up again and this time select 214ft for minimums. Another approach, minimums call, runway lights in sight, continue/land.

True story (but with different minima values - I think they set 330 instead of 321 in the real scenario).

In China you need to follow the NAIP. I understand your question links to international operation, but there is some nice news to you: (TLDR - it does matter).

Because setting a precise number such as 213 is somewhat meaningless, some other providers (different from Jeppesen) round up to the next whole 10'. Lufthansa Systems NAV definitely, for their LIDO charting product. Many huge airlines have flown with those charts long decades using this solution and never had a problem worth rediscovering the wheel.

Second, compare a NAIP chart with DA in feet to a Jeppesen Chart for one of the domestic airports. You will see the CAAC also rounds the number to whole 10' - but somewhat surprisingly - NAIP round numerically, down or up! E.g. the DA of 213 is printed in NAIP as 210 while Jeppesen references 213 (and where LIDO charts would have 220).

So, clear as mud! Happy Spring Festival and stay safe in the busy weeks.

Hi hawjl

I'm not quite sure why the rounding of the published minima changed, from memory Aerad (as was) published the minima rounded up to the next 10ft until about 2011 and I think Jeppesen might have changed around the same time.

PANS-OPS ICAO Doc 8168 states: "Publication of OCA/H. An OCA and/or an OCH shall be published for each instrument approach and circling procedure. For non-precision approach procedures, either value shall be expressed in 5-m or 10-ft increments by rounding up as appropriate." I am not aware of (and can't find) any similar wording for precision approaches but I do wonder whether that wording from PANS-OPS, or a previous version of it, combined with traditional instrument displays, gave the initial impetus to the rounding up.

Personally, I can't recognise much less than 10 ft on analogue or EFIS displays so I have stuck to rounding up to the next 10.

Cheers
TeeS

I can see some benefit in rounding up if you fly an analog aircraft. But in a modern cockpit, with digital entry of minima and auto callouts, what's the point? Why not go with the official number? What was on LIDO's mind when they decided to round up our minima?

The analogue aircraft (737CL) in the fleet when it was a in-house product? Fed-Ex customer feedback (or was it UPS?) very analogue?

And you don't get fingerslips / brainfarts 219 > 291 that go unnoticed when fatigued. Or less chance of.

But then my point was CAAC rounds down. :E

Good point

Or sticking DA in the RA spot… :E

My aeroplane is fully capable of accepting 350 DA into the RH prompt. :D

In lieu of 356.

Even worse and deadly, sticking the RA figure in the DA spot.

It’s also worth noting that while the OCH should be rounded up to the nearest 10’, those pesky surveyors have gotten more accurate!

When we add 350’ (for example) to our 13’ field elevation we get a minima of 363’. Should we just revert to using QFE to regain the lost 7’ after the second rounding? And of greater magnitude, what about the altimeter setting? We could be missing almost 30’ for a millibar/hectopascal that’s about to change! If we switch to inches Hg, it would be a maximum of 10’.

Maybe some are missing the big picture? The procedures devised cannot hope to be absolutely precise, just follow your Ops Manual procedure. And if you’re writing your own ask the lawyers…

Good luck.