RA fail on B737

[B737MRG]

You are on your way to a destination that has low visibility and en route one Radio Altimeter fails.

- there is no NNC in the QRH

- the "table of requirements" in the OM of my airline says I need both RA for any A/P approach, CAT I, II and III, so my minima become CAT I manual flight

- if I read the MEL (not applicable in flight...) it says "do not use associated A/P for approach", which means that we could perform a single channel CAT II

Any info ?

[I-2021]

Originally Posted by B737MRG

You are on your way to a destination that has low visibility and en route one Radio Altimeter fails.
- there is no NNC in the QRH
- the "table of requirements" in the OM of my airline says I need both RA for any A/P approach, CAT I, II and III, so my minima become CAT I manual flight
- if I read the MEL (not applicable in flight...) it says "do not use associated A/P for approach", which means that we could perform a single channel CAT II
Any info ?

Hi,

according to my Ops manual, you can perform a single channel CAT I since the radioaltimeter associated to the autopilot in use must be operative. For a CAT II you need 2 radioaltimeters according to my Ops manual. Of course, if you perform a single channel CAT II the airplane does not recognize the difference but from the operational point of view you are in troubles since your primary reference is the radioaltimeter and you do not have the chance to crosscheck the data. Other interesting features I am reading right now (thanks for the question anyway !) is that the RPR will remain in high state if you do not have a valid RA signal or a disagreement between 2 RA.

Just my 2 cents

[BOAC]

I'm pretty sure that JARops will not allow anything below Cat I manual landing in that condition. What does your ops manual say, MRG?

[B737MRG]

As I said, our Manual doesn't allow me to use the A/P for approach, even no CAT I.

[I-2021]

So you Ops man brings in an additional limitation, that's it

[alexban]

B737, I think you may have read it wrong .The a/p is not allowed to be used for app,meaning the a/p the same side with the failed RA. You may use the other one,no restriction for that.
We have the same info,and this is the way we understand it.
So,left RA u/s ,you should use only the right A/P for the app,CAT I only.
Also,for CAT II or III we have to do only autoland- so no CAT II or III availability with one RA u/s.

[RYR-738-JOCKEY]

I agree with alexban. BTW for cat 1 there is no requirement for an RA in the first place.

[I-2021]

Originally Posted by alexban

B737, I think you may have read it wrong .The a/p is not allowed to be used for app,meaning the a/p the same side with the failed RA. You may use the other one,no restriction for that.

I think he understood that. May be what he means is that either autopilot cannot be engaged according to his ops.

We have the same info,and this is the way we understand it.
So,left RA u/s ,you should use only the right A/P for the app,CAT I only.
Also,for CAT II or III we have to do only autoland- so no CAT II or III availability with one RA u/s.

In CAT II you must do an automatic approach but landing can be manual, therefore you can perform a single channel CAT II. The point is that with one RA failed you are still able to fly single channel but limited to CAT I due to JAR OPS requirements.

[I-2021]

Originally Posted by RYR-738-JOCKEY

I agree with alexban. BTW for cat 1 there is no requirement for an RA in the first place.

That's it, but you have to fly it manually without flight director

[B737MRG]

I have checked my Ops Manual again and it clearly states that we require both RA for an A/P approach, doesn't matter which A/P.

[alexban]

then,i guess a/p approach must mean autoland.If this is the case,I agree...you should have both RA to do it..
I-2021...our SOP does not allowe for manual land at cat II,even if the AFM permit it.Only autoland..

[I-2021]

Originally Posted by alexban

then,i guess a/p approach must mean autoland.If this is the case,I agree...you should have both RA to do it..
I-2021...our SOP does not allowe for manual land at cat II,even if the AFM permit it.Only autoland..

Ok, maybe that's the point. Our SOPs allow for CAT II auto approach and manual land with AP disconnect at published RA minima. The advantage is that you can go down to CAT II minima on single channel. I know that some operators require both autopilots for CAT II approaches anyway.

[B737MRG]

I am not native english speaking, therefor I'll try to explain it again :

- according to our OM, with 1 RA failed, you may not use ANY A/P in Approach Mode.
- if I read the MEL, it seems (technically spoken) I could perform a single channel A/P approach. Autoland or not, CAT I or CAT II, this is not really my question, this is rather company regulations than technical stuff

Now my question is ; are there any other companies that require BOTH RA when using ANY A/P in Approach Mode ? The explanation within our airline is that the A/P uses information from both RA through crosswiring, so whatever A/P you use for Approach Mode (disregard the autoland), it requires both RA to be functional.

[alexban]

As far as I know,the RA's are dedicated for their side A/P.
For ex.:
When performing a dual a/p autoland app,in case one RA fails bellow 500',let's say at 200' you'll have no caution untill 50'RA.At this point one a/p will try to flare ,while the other one won't (cause no RA signal).The system will sense the difference in a/p actions,and the a/p's will be disconected.
I had the RA u/s on one side twice,did a cat I app,no problem whatsoever.
I've checked the FCTM,and I couldn't find no RA requirement for catI app.Actually,you're not allowed to use RA at catI for minima,it's a MDA approach,so QNH only.
I hope I didn't say anything silly here,it's a bit late,and my 3 yrs old sun it's dancing on my head right now,to stop writing and start playing some game...
Brgds
Alex

[Cap Loko]

How can you go down to CATII minima on one channel?
According to FCOM vol I, the Minimum Use Height for single channel autopilot operation is defined as 158 feet AGL.

[B737MRG]

I am aware of the MUH, but several companies allow single channel approach in CAT II

[I-2021]

Originally Posted by Cap Loko

How can you go down to CATII minima on one channel?
According to FCOM vol I, the Minimum Use Height for single channel autopilot operation is defined as 158 feet AGL.

Hi,

On AOM Vol.1 "limitations" section L.10.4 date June4, 2004 it says : For single channel operation, the autopilot shall not be engaged below 50 ft AGL.