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Terrain clearance on an amended missed approach

I think it’s fair to say that 99.99% of instrument or visual procedures built around an instrument runway are designed assuming no turns bellow 400ft agl (departure? and circling?), those that require under that will likely have VMC restriction or ceiling minima

I make sense to pick that as 1) sensible personal weather minima even for straight-in departure in case they need to turn for some reason or 2) take ATC vectors or directs bellow MSA

Last Edited by Ibra at 05 Sep 13:04
Paris/Essex, France/UK, United Kingdom

gallois wrote:

I don’t recall ever saying it was a legal requirement to climb to 400ft before turning on an omnidirectional departure.

I don’t know about “legal requirement”, but according to PANS-OPS, departures (both SIDs and omnidirectional) are designed with the assumption that the aircraft does not make any turns below 400’ AAL (not AGL). If obstacle conditions require straight flight to a higher level, that level shall be promulgated.

ESKC (Uppsala/Sundbro), Sweden

Thomas28 wrote:

The alternative is to not accept this instruction below the MSA as published on the approach plate and instead follow the published missed approach until reaching a safe altitude. But that will cause chaos if the deviation was for traffic from another runway or something like that.

At a towered airport in the US, one rarely flies the published missed approach procedure. Once ATC provides a vector, they are responsible for terrain and obstacle clearance. Failure to follow an ATC clearance will most likely result in a pilot deviation.

KUZA, United States

Failure to follow an ATC clearance will most likely result in a pilot deviation.

It would here too.

Shoreham EGKA, United Kingdom

Ibra wrote:

400ft agl is bigger fish to fry: it’s necessary conditiom but it’s not sufficient likely no one understands what that 400ft agl is about but one hears it regularly from airliners pilots or some instructors from time to time out of the topic, @gallois told me last time I need to remain VMC untill 400ft agl on non-instrument departures as well

First, don’t you need published departure (SID or OMNI/ODP) or approved departure (airliners mannual) to turn at 400ft agl? or sometimes bellow 400ft agl !

My understanding to make specs for obstacle clearances in published departures, the TERPS & PANS-OPS make load of assumptions on how high an aircraft cross runway end (35ft HGT), how much deg on runway track (15deg TRK), how many engines it has and what performance class it is, how early they can turn (400ft) and how much bank angle they can take (15deg AOB)…all this does not mean one should turn off route on ATC vector at 400ft agl?

However, if it’s an instrument runway with published omnidirectional departure up to 400ft agl, why not?

Also, ATC assumes rate one turns for vectors, the published turns at low level may specify own bank angles and speeds !!!

A straight ahead missed approach procedure in TERPS requires a 40 to 1 surface to be evaluated for obstacles out to 15 NM and assumes the aircraft will climb at the standard rate of 200 feet per NM or greater.

Here is the TERPS criteria for a turning missed approach and is where the 400 feet before a turn comes from:

2-8-6. Turning Missed Approach Area. If a turn of more than 15 degrees from the FAC is required, a turning or combination straight and turning missed approach area must be constructed. If the HAT or HAA value associated with the DA/MDA/CMDA is less than 400 feet, construct a combination straight and turning missed approach (see paragraph 2-8-8). The minimum turn altitude is 400 feet above touchdown zone elevation (TDZE)/airport elevation, rounded to the nearest foot increment

Although similar to a DP, the missed approach criteria has its own requirements. When the standard climb gradient can’t be met, either the DA/MDA is increased or the minimum non standard climb gradient is specified in a note.

KUZA, United States

Thanks that adds nicely, the 400ft AAL applies to all turns in both missed & departure designs altough each has own specs, does it also apply to TERPS circling? (in PANS-OPS min height for circling is 400ft AAL)

Paris/Essex, France/UK, United Kingdom

Circling has a minimum circling MDA based on the NPA MDA or 350 feet above the highest obstacle in the circling area for the category, which ever is greater. Circling is not supported from a vertically guided approach such as an ILS/GLS/LPV/LNAV/VNAV, so the procedure must have an NPA option. Sometimes the circling altitude is below the vertically guided procedure, this occurs mostly when the procedure is published with an LPV and an LNAV/VNAV and an LNAV option, where the LNAV/VNAV DA is above the straight in LNAV and CTL MDA. IOW, you have to fly the procedure as an NPA to the MDA.

KUZA, United States

Failure to follow an ATC clearance will most likely result in a pilot deviation.

I didn’t mean just ignore it, I meant saying you’re unable due to obstacle clearance at the point you’re given the amended instructions.


I would agree with the procedure, but time and time again, reading accident reports, it has become clear that the vast majority of pilots have nothing in their cockpit which tells them where terrain is. No topo depiction, no GPWS, no SV, nothing. Easy to confuse left/right and go straight into some rock. I met a guy recently who gave up flying after four of his friends flew in an SR22 left instead of right.

ATC are not always right, especially in certain southern countries, but they are much more likely than a pilot to know where the rocks are. They after all do this all day, while the GA pilot has rarely if ever been to that airport before.

Shoreham EGKA, United Kingdom

The trouble is you could never regulate for people who can’t differentiate left from right under pressure.
As pilots we have for many years had ways of avoiding terrain. They are called charts and are why you should brief an approach.
Technology like GPWS is a useful tool but should not become mandatory or essential.

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