B737 RAIM or AAIM

[pilotnik86]

On every website I find it says B737 uses RAIM to augment GNSS signal. Does anybody know where can I find a proof? Any kind of evidence officially signed by Boeing.
There are two types of ABAS: RAIM and AAIM. The AAIM definition suits B737 like a glove, yet literally everyone writes it uses RAIM. I've been asking myself this question for years. Can someone help?
If someone has any evidance on Airbus being or not being equiped with RAIM, that will do the trick too.

Why is it important? If it's RAIM the aircraft is banned from RNP approach during RAIM unavailability. With AAIM there is no such case.

[poldek77]

I'm not sure if it can satisfy you - FCTM (definitely Boeing document :)) says on page 5.66:
The ANP is an FMC calculation based on RAIM, method of updating, and other factors, and constantly fluctuates in value.

[Checkboard]

For the Airbus


https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1744x1120/screen_shot_2020_11_14_at_22_08_17_f749607946dd8335ba529f5b7 7158806b5872381.png


https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/1730x482/screen_shot_2020_11_14_at_22_09_16_520645280531e775be7bf00ad 5e93e05fdfd7947.png

[FlightDetent]

? The M in RAIM stands for MONITORING.

I.e. RAIM is a self-diagnostic tool, not an augmentation service.

[pilotnik86]

Thank You. I guess that must suffice. Still I can't understand how some EU airlines operating on B737 tell their pilots that they can perform RNP approach (LNAV & LNAV/VNAV) even during RAIM unavailability. This is the key reason why I asked this question.


? The M in RAIM stands for MONITORING.

I.e. RAIM is a self-diagnostic tool, not an augmentation service.

Sure it is. RAIM is one of two types of ABAS. The other one is AAIM. You can get more details from Annex 10, DOC 9613 and 965/2012 Part-SPA. What the M stands for is completely irrelevant.

[FlightDetent]

Surely sure?

[STBYRUD]

Thank You. I guess that must suffice. Still I can't understand how some EU airlines operating on B737 tell their pilots that they can perform RNP approach (LNAV & LNAV/VNAV) even during RAIM unavailability. This is the key reason why I asked this question.




Sure it is. RAIM is one of two types of ABAS. The other one is AAIM. You can get more details from Annex 10, DOC 9613 and 965/2012 Part-SPA. What the M stands for is completely irrelevant.
Whats your point? Since the 737 in incapable of RAIM prediction itself the operator must at least use some kind of external RAIM prediction service, such as AUGUR, to dispatch aircraft in conditions that would require a certain RNP approach or procedure. If in flight RAIM causes the ANP to shoot up above RNP for the procedure, either because of signal unavailability or other reasons, you obviously can't shoot the approach...

[pilotnik86]

Whats your point? Since the 737 in incapable of RAIM prediction itself the operator must at least use some kind of external RAIM prediction service, such as AUGUR, to dispatch aircraft in conditions that would require a certain RNP approach or procedure. If in flight RAIM causes the ANP to shoot up above RNP for the procedure, either because of signal unavailability or other reasons, you obviously can't shoot the approach...

Yes, but you must realize there are entire FIRs in EU and airlines (I believe DLH is one) in which RNP approach is banned during RAIM unavailability promulgated by NOTAM. On the other hand there are airlines who teach and examine their pilots that they can attempt an approach even during RAIM unavailability. So there is a major inconsistency in the area. Someone has to be wrong.

If it is in fact true that a crew is only dependant on the ANP value than what is the point in banning the approach? In case of RAIM loss the ANP will rise, the G/A criteria will be met. But there is more to it than this. The B737 FMS is computing its position based on GNSS, DME/DME, INS and VOR/DME (this one is not even allowed any more on most SIDs and STARs). I can't confirm this but it sems like the latter three systems are considered in the positioning eqation until the aircraft is powered down. So they work just fine during the RNP approach and can augment the positioning. The problem is that they shouldn't. The RNP approach cannot be executed with other than GNSS positioning sensor unless specifically authorised by state (which is rare). I haven't seen single pilot who switch off DME/DME, INS and VOR/DME during the approach in order to have pure GNSS-generated ANP. So it might happen that despite the lack of RAIM the ANP will not rise or rise very slowly. I can't say I have it all right since I can't find any proof but certainly some FIRs/airlines forbid the approach in case of RAIM loss and some don't (some even encourage their crews to try!). I can't figure out why.

[FlightDetent]

You are mixing apples and oranges, sir. Reading the materials you already have could help, focusing on what they are actually saying as opposed to one's self first perception. Otherwise a brief from someone well acquainted with the inner logic and dependencies is required.

What people do and don't on the line, in the SIM sadly even sometimes teach, may not be strictly in accordance with the approved materials, i.e. OM part B. Yes, tough. :bored:

[pilotnik86]

You are mixing apples and oranges, sir. Reading the materials you already have could help, focusing on what they are actually saying as opposed to one's self first perception. Otherwise a brief from someone well acquainted with the inner logic and dependencies is required.

What people do and don't on the line, in the SIM sadly even sometimes teach, may not be strictly in accordance with the approved materials, i.e. OM part B. Yes, tough. :bored:

I asked the question not because I want to read "you need to read more" because it is extremely hard to find more. I asked this question to find someone who knows the answer to why there is an inconsistency and is able to logically explain. While I appreciate Checkboard and poldek77 contribution I honestly can't listen to someone who does not want to elaborate past "you are mixing apples and oranges" and openly claims that RAIM is not a type of augmentation.

[FlyingStone]

The RNP approach cannot be executed with other than GNSS positioning sensor unless specifically authorised by state (which is rare). I haven't seen single pilot who switch off DME/DME, INS and VOR/DME during the approach in order to have pure GNSS-generated ANP.

Have you got a reference for that? AMC 20-27 and 20-28 specifically allow the use of integrated navigation system incorporating a GNSS sensor, provided it is certified, etc.

You might be confusing things with RNP AR, which does not allow reversion to DME/DME, unless the operator is specifically approved. Boeing RNP AR procedures (at least for the 737) require crew to inhibit VOR position updating prior to commencing such approach, with DME updating to be inhibited as well if required.

At least on the 737, there is no way to inhibit IRS position update as such, but its bias is set so low that ANP would skyrocket well before position would drift towards IRS only.

[FlightDetent]

that RAIM is not a type of augmentation. I can see how the definition of ABAS in EU-OPS as led you astray, its suggestive last sentence is occluding the principles, although it does say what you quoted already.

RAIM definition is much clearer ‘Receiver autonomous integrity monitoring (RAIM)’ means a technique whereby a GNSS receiver/processor determines the integrity of the GNSS navigation signals using only GNSS signals or GNSS signals augmented with altitude. This determination is achieved by a consistency check among redundant pseudo-range measurements. At least one satellite in addition to those required for navigation has to be in view for the receiver to perform the RAIM function.

RAIM is not improving the GNSS signals, nor adding another source for position calculation, but merely a monitoring tool. Assuming otherwise will lead to doubtful findings that at some point, where I believe you may have already arrived, stop making any sense. The answer you need is not available until proper names and meanings are used, no matter whose fault they might be.

I.e. "GPS Required" do not specifically mean "INS (VOR/LOC) not permitted". The FMS/MMR internal logic will take care to use the most accurate and reliable coordinate source - and in such voting process RAIM is essential.

[poldek77]

(...) I haven't seen single pilot who switch off DME/DME, INS and VOR/DME during the approach in order to have pure GNSS-generated ANP.

Sorry to disappoint you - in my outfit we really leave GPS as the only source for position updating as a standard part of preparations for RNP approach. And we do not have any problems with it.