Low Height Warning during R/W GCAs - What height do you set?

[greenhaven]

Had an interesting(ish!) discussion in the crewroom today reference setting the height warning bug on a GCA approach, and just wondering what the general consensus was? (RN Merlin aircraft in question)

Currently setting 100 ft on PAR, 200 ft on SRA, regardless of DH or MDH (in fact about to be standardised to this) The argument was whether it's a good idea to set the bug at DH (ie hear the warning, look up for sight, etc) , set it at an arbitrary value below that (say 10% below DH, in case of messing it up) or even not use it at all...

Any thoughts?


:confused:

[A and C]

Most civil aircraft that are fitted with a rad alt have a the ability to set a warning height and it is common practice to set this at the DH .
It would seem to me that a warning that it is time to decide to land or go around cant be a bad thing.

[MG]

The Chinook fleet has a RadAlt with a noise and a light warning. We (and I think SH as a whole) set the light to the DH/MDH, adjusted for the pilot's rating, and the noise to 200' for a non-precision app or 100' for a precision app. Seems to work, we haven't crashed one from an approach yet! (Touch wood!!!)

[Hezbollah]

Sea King Mk 4 SOP is based on the idea of the RADALT as a ground proximity warning system (in commonality with NVG/maritime ops) as opposed to a DH/MDH reminder. Because we try to link the idea of the warner going off with pulling power and getting away from the ground, we dont want it until after we have made the definite decision to land. Therefore, we use 100' for any GCA, and 1000' set on the NFP side for an IF transit, and change selection between the two on climbing through 1000', or on pre-landing checks. It seems to work, and makes sense, because we should be scanning the Baralt for the DH/MDH anyway, in preference to the RADALT.

[ShyTorque]

Jeppesens publish the minima as MDA (MDH).

We use QNH for landing and set the MDA (on QNH) on the altimeters and the associated MDH on the radalt.

They should be reached at about the same time, obviously subject to terrain on the approach path. The radalt is the most important one, as it responds to the lumpy bits that hurt.

You chaps are presumably still using QFE for landing though?

[SASless]

Wash yer mouth out Shy......they get frightfully picky about the QFE business! Wonderful thread in the past about that....pprune fishing at its best! I always thought the decision was made based upon BarAlt....and the RadAlt was used merely as a backup.

Try to set QFE in Denver or Lead sometime! Only reason we don't use the QFE routine is we have trouble reading two altimeters and having three BarAlts would invite mutiny from the cabin staff or whoever else would think they could use it for theirs.

I forget....we have a pilots Altimeter, a copilot's altimeter.....what the heck is the third one called.....? Let's see...Co is on Airfield QNH...Pilot is on QFE....third one is on....errrrr....Regional QNH...now if we transfer handling during the approach for some reason....do I set mine to local QNH and Co's to QFE or.....???

[BHPS]

The civil rotary community tend to use the following with their rad-alts:

Precision Approaches - DH-50ft
Non-Precision Approaches - MDH-100ft

That works very well.

BHPS

[ShyTorque]

SASless, I'm entitled to ask as an ex crab, I'm not fishing this time.

BHPS,

That's rather a generalisation. We don't do that. What criteria are you using for your minima? They are very low, certainly below JAR minima.

[Pub User]

MG and Hezbollah indicate a similarity between SH and the SK4 fleets. On SH the Radalt Audio is set to 100' for precision and 200' for non-precision, purely as a ground proximity warning.

This is because the Radalt reading may bear no relation to the DH, due to possible terrain contours on approach, but it is (as shyTorque states) the important one when it comes to not hurting yourself.

It's a while since I've done one, but I seem to recall a precision approach at Shawbury gets the radalt down to 200' a mile or two before DH, which could be a cause for confusion if you were using it as a go-around reference. At Leeds-Braford (SW rwy), conversely, the radalt sits nicely high until a few yards before the threshold, when it rockets downwards to match the QFE height.

[Tourist]

If you're a pinger its simple.
Don't set the bug, and we don't have an audio warner.
much easier!:D

[BHPS]

ShyTorque

As I undersood it, the question was what to set the rad-alt bug to. In my Company the non-flying pilot's bug is set to Decision Height minus 50ft (so for an ILS with a DH of 200ft, the bug would be set at 150ft), and for a non-decision approach Minimum Descent Height minus 100ft (so for a NDB approach with a MDH of 400ft, the non-flying pilot would set 300ft on the rad-alt).

The flying pilot is entitled to set what he (or she) wishes so long as it is NOT lower than the non-flying pilot's bug.

I suspect that is probably what your Company does and you probably mis-interpreted my "DH -50" and "MDH -100" phrases in my earlier posting. Does that now clear the matter up? As my Company is JAR-Ops compliant I can assure that we are within JAR Ops 3 regulations.

As an ex-RAF helicopter Procedural IRE, I seem to remember that this was the settings that we used as we had been civil trained for Procedural flying. However, that was about 15years ago, and as it is all done in house now, that may have changed.

[extpwron]

In the RAF SAR Force we set 125 for a Precision approach and 225 for a Non Precision approach. (In the RAF Sea King, both Rad Alts kick off with light and audio at which ever pilot has the highest set)

That is 25 below the absolute minima of 150 and 250 for Rotary Wing approaches.

Bear in mind that at decision height you will, by definition, descend briefly below the datum as you execute the go around.

The other considerations are that “checks waste time” and “don’t chicken out at decision height”!!

[ShyTorque]

BHPS,

Yes, I took the second use of your "-" to mean the same as the first and I mistakenly thought you were saying that the 50 ft and 100 ft were the DA and MDA :eek:

Gotcha drift now, thanks!

Does anyone have a proper round altimeter with an audio / visual reminder of required minima though? The only ones I have seen are flimsy plastic reminder tabs on the bezel that are often worse than no use as they rotate off the set position with airframe vibration.

[flygunz]

It's clear from the posts that all of 'us' use the low height warning system to assist on GCA approaches albeit in slightly different ways. I've never been a fan of using the a height warning system to 'aid' a GCA approach for the simple reason that's not its purpose and would discourage its use on Instrument tests. The reaction to a pre set height warning should be to climb away from the danger area. By day it's not so much of an issue but at night on any of the NVS its critical.
I've always found that good SOPs for GCAs and the like negate the need to use non related equipment.
Not preaching but have my doubts.