Radio altimeter setting on CAT I and non-precision approaches

[teesix]

This question applies to B737 Classic:

What radioaltimeter setting (if any) does your company SOP prescribe on CAT I and non-precision approaches?

[Denti]

Standard procedure is -20ft, so you will get no RA call at all in my outfit.

[teesix]

Thank you! Exactly my argument too!!!

[Capn Bloggs]

Not a 737, but in our outfit we use the Rad Alt call as a final backstop against IMC descent below the minimum (whatever that may be).

For a Cat 1 ILS, we set it at 150ft.

For an NPA, we set it at 300ft.

When the Rad Alt calls "Minimums" an immediate go-around is mandatory unless the PF has obtained Visual Reference.

On a visual approach, we set it to zero to stop it calling.

[BOAC]

-20 in BA UNLESS a Cat I rad DH is published (I seem to recall 06L at MAN had one). There is an old thread somewhere in Pruneland about setting radalts for backstop terrain checks on NPAs, eg the 300 as above, which should also be a safety check on any ridges/hills on the approach.

[Spooky 2]

300' for TERPS min terrain clearance mins. Any RA verbals or inducations prior to breaking out calls for a MAP.

[PT6A]

My outfit(s) have always been the ones to tell us to set it to the minimums.... keeping in mind that for CAT I / NPA that the minimum is based on baro.

But I think in reality all it does is lead to people using the RA when they should not!

Also.. one time in the sim I was doing a NPA with several failures on the go and the "minimum" call went off causing me to do a go around when I needed not!

So all in all I don't think we should use it unless we are doing a CAT II or better.

Really will be quite interesting to see what everyone else is doing though!

[742]

The world is a lot lumpier than most simulator databases model, and I think this subject is a good example of how the simulator world can negatively influence operating procedures.

I like the method used by Capn Bloggs, and IMO it is the only one that can work reliably on the line.

[Pilot Pete]

So all in all I don't think we should use it unless we are doing a CAT II or better. Do you mean CAT II or worse (i.e. CAT III etc)? What about where it is a CAT I approach with a Rad Alt DH?

I like the method used by Capn Bloggs, and IMO it is the only one that can work reliably on the line. The only one that can work reliably? So setting a negative value (as many, many operators do) doesn't work reliably?

PP

[latetonite]

As far as I know a rad alt is not part in the flying of a cat I approach. End.

[PT6A]

Yes Pete!.. thats what I ment.. I was thinking better approach (as opposed to worse weather!)

I too like Blogg's approach as it does provide a bit of a safety net and removes the distraction of it providing an incorrect (except for cat II/III) "minimums" call.

I have seen many pilots fall foul of this on a dark and stormy night to have "minimums" screamed out when it is not the correct time serves no purpose IMO.

[Mach E Avelli]

Bloggs' Company has it spot on. I was there when it was introduced, after much debate with old diehards who didn't want it because it 'wasn't invented here' (the 'here' being a certain large Australian airline no longer trading).
It is based on a Flight Safety Foundation recommendation to use all tools at your disposal to prevent CFIT. The paper is still available from the FSF website and is worth a read.

[ZFT]

The world is a lot lumpier than most simulator databases model, and I think this subject is a good example of how the simulator world can negatively influence operating procedures.

With the latest sims deriving real world terrain heights from satellite data, this should no longer be an issue.

Older sims were/are pretty poor with terrain heights 'computed' from a variety of methods such as utilising closest nav aids heights as the reference.

[transducer]

With EGPWS becoming the norm in most airliners this is a further and even better safety net than setting an arbitrary height on the radio alt. that might/might not protect you. EGPWS has a terrain clearance floor function that generates alerts based upon current airplane position, nearest runway centre point position, radio altitude, and a database of hard-surfaced runways whose length is greater than 3500 feet. Penetration of the alert envelope activates the GND PROX lights and generates a “TOO LOW TERRAIN” aural.

[Spooky 2]

All true but I think our original poster was probably refering to an aircraft that had something less the "enhanced" GPWS. Keep in mind that most of the new aircraft your either in in the bro mode. or RA mode and you cannot set your RA for any type of alert. The classic's don't typically have that configuration. Setting the RA for say 300' is simply another tool that the professional can use should he want. No harm no fould assuming it is approved by the operator and briefed prior to the approach.

[PEI_3721]

Simulator databases: - if your simulator has EGPWS, check that the equipment used is a ‘real’ EGPWS box.
If so, then the simulation should have the appropriate terrain databases for free (check database currency and EGPWS software mod state). The sim may require a simple configuration change / wiring mod.
When EGPWS was first used in simulators, a few operators had some surprises when flying their specific engine out procedures – emergency turns etc. Only with the EGPWS / terrain database did they realize how close you can get to ‘real’ terrain. One operator discovered that a particularly ‘difficult’ procedure did not provide terrain clearance at all.
The EGPWS database should also provide (simulate) accurate Rad Alt displays.
This is a display which IMHO should be included in the instrument scan during all approaches – it is a display which aids situation awareness. Rad Alt callouts, alerts, etc are additional awareness tools. Ensure that theiry are used and their applicability briefed before the approach is started; don’t discard them because the approach is not Cat 2/3.
Don’t forget visual approaches (and take off) – see incidents # 7 & 8. (http://www.icao.int/fsix/_Library%5CTAWS%20Saves%20plus%20add.pdf)