IRS fast realignment

[jorgvaz]

Hi, please could anybody help me on this topic?

In wich circumstances is proper to perform a fast realignment procedure??

Thanks in advance!

[CaptSnails]

Anytime you may have residual ground speed. Fast realignment permits you to zero ground speed and enter a new present position. In some instances a full allignment is required, for example if the flight is planned to go into RVSM airspace.

[Dom Joly]

We used to do a fast realign in the turnarounds as we often only had 30 mins. Dont have IRS on our a/c anymore (different a/c). Im not aware of a requirement to do a full IRS alignment if going into RVSM - I changed whilst RVSM was being introduced. If we had a long turn around 1hr+ we might do a full realign or if there was a noticeable problem with the IRS's e.g. wander. The a/c position will update when you press the TOGA button for Take Off to the Rwy threshold (or displaced threshold if you enter that in the FMC's). They should as far as we are concerned be positionally as accurate as each other (full vs. fast).

[FlapsOne]

Full alignment only takes 7-10 mins - what's the problem on a 30 min turnround?

[TopBunk]

I seem to recall a technical memo in the company I fly the A319/320 for coming out in the last couple of months actually encouraging 'fast' re-aligns rather than full re-aligns on transits.

Can't remember the reason (don't really care if the truth be told).

[Dom Joly]

7 - 10 mins in which you can't get a visual representation of the route. We were encouraged by the training dept to use 'fast realigning' to aid turnaround time. This was especially the case if we were late arriving or had a 'tight slot'. Our FMC's were rather old & had a small memory capacity. As a result only the regular departure SID's & STAR's remained in the database. Therefore, if we had a different SID than the one in the FMC we would have to construct it ourselves. With some airfields having complicated procedures like Milan the extra 7 mins was often invaluable!

[QAVION]

"7 - 10 mins in which you can't get a visual representation of the route."

Didn't your aircraft cockpit navigation displays have a PLAN selection for viewing the route? (On most glass cockpit aircraft, no IRS alignment is required to view the route on the PLAN page). MAP, on the other hand, is a different story.

Cheers.
Q.

[ECAM Status]

Airbus in their FCOM3, recommend NOT to do any realignment of the IRS's if the residual groundspeed of the 3 IRS's is less than 5kts. If even 1 IRS has a residual groundspeed of 5kts or more, a quick realignment must be made. That is for transit stops.

Also, FCOM3 says " For flights with long segments on which there is no updating of FMGC position with radio navigation (i.e. over the North Atlantic MNPS airspace, especially if the aircraft is not equiped with GPS), perform a complete alignment. For all other flights a quick alignment is sufficient. ADIRS PERFORMANCE MAY BE DEGRADED IF COMPLETE ALIGNMENTS ARE SYSTEMATICALLY PERFORMED.

Hope it helps.

[Brenoch]

I think the MNPS area is what Capt Snails is refering to rather than RVSM. The only thing you won't get on a fast realign versus a full one is heading update.

I think thats what it comes back to with the MNPS, to have the most accurate heading possible..

My two p.

Regs

[SuperRanger]

on the 73 classic that i used to fly, we used to do a full-align on every stop but then the rate of IRS failures started to go up. from recommendation of engineering, we then switch to a fast-align on transit of less then 1 hrs (or there abouts).

on the current 777, there's no fast-align for the ADIRU's so the recommendation is a realignment every 24 hours.

SR

[TopBunk]

Superranger

on the 73 classic that i used to fly, we used to do a full-align on every stop

The 737 Classics (ie the -200) that I flew did not have IRS's, so I suspect that you are not really talking about the 737 Classic at all.

[Down...2 greens]

TopBunk,

According to Boeing's terminology the 737-100/200 were the 'Originals', the -300/-400/-500 were the 'Classics' and the -700/-800/-900 are the NGs.

[Wizofoz]

D2G

And the 600!! Don`t forget the 600!! Nobody ever remembers the 600!!!

Anybody actually bought one???

[Chill]

Quickies

In the States we got told (as in "do") ... "There's always time to do a full re-align - so do it." ... which is all well and good when you're on Ver 10+

Now operating on Ver 1.6 (so slow I can go to the fwd galley, make a coffee, come back and it's still computing performance) so Dom Joly's comment is sadly all too true, minutes become precious - and re-entering SIDs gets a little tedious

And hey - QAVION - some of us are still getting around in "hardballs" mate and I still haven't found a way to transfer RTE PLAN data to the WX radar actually I'd probably have more success reading it in the coffee granules in my cup

We do a quickie just prior to pushback (to zero any errors from - particularly extended - gate time) and another at turnaround unless we're there for more than 30-40 minutes.

[TopBunk]

D2G

'737-100/200 = originals, 733/4/5 = classics.'

That's news to me. Ah well, we live and learn.

So, following on from that what are the 741, 742, 743 known as? I have always refered to the 741 & 742 as the classics, are they also now the originals too?

[jorgvaz]

Thank you all very much for the info. It is really appreciated.

[The Puzzler]

Puzzle me this....

Sorry to drag this out of the archives but a quick question regarding the need to perform a quick align on the 737NG. On 30 min turnarounds is it necessary to do any realigning or is it OK to just enter the airport identifier and cross check the last position in the FMS vs our present position. I fully understand what a quick align does re: groundspeed etc but this question relates to what is the general norm amongst other NG operators.

Thanks in advance

[Wizofoz]

Puzzler,

Whilst the FMC position should always be updated via the GPS, the IRS platform has many other functions, so re-alligning it is a good idea whether fast or slow..one obvious one being that I think (and I stand to be corrected) that the Ground Speed readout and Wind calculation are purely IRS.

[The Puzzler]

Puzzle me this....

Wizofoz,

Thanks for the reply. You're correct in relation to the groundspeed and wind, which is one of the reasons I'm all for at least a fast align on short turnarounds and a full align when time permits. From what I can ascertain the GPS is extremely accurate at position fixing (assuming good satellite coverage) but this alone should not determine whether we realign or not. We are, as you correctly say, zeroing several other 'errors'.

[MasterBates]

FlapsOne sais:

Full alignment only takes 7-10 mins - what's the problem on a 30 min turnround?

If after full alignment, just before pushback you notice g/s on the IRS, simply do a quick align. It doesn´t do any harm, just stops the groundspeed and the gate position can be re-entered.