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European Airlines And Full IRS Alignment  
User currently offlineseven3seven From United States of America, joined Apr 2005, 318 posts, RR: 23
Posted (1 year 10 months 3 weeks 2 days 17 hours ago) and read 3502 times:

In all the pics of European airliner Boeings at the gate I notice what looks like a full inertial navigation system alignment everytime. At my airline we just do a quick align of the system between flights during the day. It takes just a few seconds as compared to up to 7 minutes with a full alignment, and we have GPS anyway.

Can anyone provide a justification for a full IRS alignment after every flight?


My views are mine alone and are not that of any of my fellow employees, officers, or directors at my company
12 replies: All unread, jump to last
 
User currently offlineairbuster From Netherlands, joined Mar 2007, 443 posts, RR: 0
Reply 1, posted (1 year 10 months 3 weeks 2 days 14 hours ago) and read 3435 times:

Hey,

We do exactly the same as you. Full alignment from cold and dark and on e.g. a turnaround just a quick align. This is on a F70/100.



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User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 2, posted (1 year 10 months 3 weeks 2 days 12 hours ago) and read 3385 times:

About all pilots I talked to did full alignment, on the 737 at least. It really makes little difference, it is not like other things are finished before 10 minutes after shutdown pass.


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User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 3, posted (1 year 10 months 3 weeks 2 days 10 hours ago) and read 3348 times:

We do a full alignment on every thru stop.

User currently offlineseven3seven From United States of America, joined Apr 2005, 318 posts, RR: 23
Reply 4, posted (1 year 10 months 3 weeks 2 days 5 hours ago) and read 3262 times:

Quoting Fabo (Reply 2):
It really makes little difference, it is not like other things are finished before 10 minutes after shutdown pass.

We are famous for 20 minute turns and often have everything done and ready to go in the cockpit in 5 minutes. Again, can anyone provide justification for a full alignment over a quick align?

[Edited 2012-10-31 22:42:55]


My views are mine alone and are not that of any of my fellow employees, officers, or directors at my company
User currently offlinestrfyr51 From United States of America, joined Apr 2012, 1216 posts, RR: 1
Reply 5, posted (1 year 10 months 3 weeks 2 days 1 hour ago) and read 3211 times:
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a full alignment clears any errors that might have built up over time. Since Drift and radial position error are all monitored in the Maintenance manual with limits it just makes good sense to do a full alignment if that's what you need. . Since 2 alignments reported bad might cause the replacement of a $300,000 part needlessly? It makes darn good sense financially to take the extra 3-5 minutes. .

User currently offlineKAUSpilot From United States of America, joined Jan 2002, 1959 posts, RR: 32
Reply 6, posted (1 year 10 months 3 weeks 2 days 1 hour ago) and read 3205 times:

Obviously I'm not European but: We do a full alignment every time; granted our average leg length is about 8 hours and the fastest turn I've ever done is 45 minutes. Going from memory, the 744 can go no longer than 18 hours of flying time between full alignments.

Reasons we turn them off after the flight and usually do a full alignment prior to the next flight:

1. After a flight, we don't know how long the airplane will sit there between the time we leave and the time the next crew shows up (and the plane almost always stays powered up with APU or external). If there was a power interruption and the plane went into standby power while it was sitting there, the IRU's could overheat if there wasn't a mechanic or someone else around to notice (normally someone should be monitoring the aircraft all the time while the APU is on, of course). The airplane is rarely powered completely down between flights.

2. We have no real way of knowing how long the previous crew went before a full alignment. Fast alignment is still an option that can be used at the crew's discretion, but SOP is a full alignment before every flight. So it's possible that the aircraft might be close to it's 18 hour limit.....there's no way to know for sure without asking the previous crew, who we usually don't see.

3. True it doesn't matter very much given GPS, but IRU accuracy is tracked by the company at the end of each flight....we have to send IRU error out as part of the ACARS post flight report. Also much of Europen airspace is RNP 5 which is easy enough to maintain on IRU's alone, so it's nice to know you can maintain RNP even if GPS is lost for some strange reason. There is no such RNP requirement in the USA's domestic enroute airspace structure, to my knowledge, so it would make sense not to worry about it as much there.


User currently offlineAA737-823 From United States of America, joined Mar 2000, 5822 posts, RR: 11
Reply 7, posted (1 year 10 months 3 weeks 2 days ago) and read 3194 times:

The catch is, if you're in WINDY conditions, the 737NG is notorious for refusing to align. For this reason, a lot of carriers won't do a full align if there's much wind at all. If you can feel the tail shaking, it's usually a bad idea, in my experience, to realign.

User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2255 posts, RR: 15
Reply 8, posted (1 year 10 months 3 weeks 1 day 22 hours ago) and read 3153 times:

Quoting AA737-823 (Reply 7):
The catch is, if you're in WINDY conditions,

I thought that was a trait of older IRSs. Wind shake doesn't seem to be an issue at least in the -11 and we see wind as well as the airplane moving when loading the freight. never had a problem.


User currently offlineDashTrash From United States of America, joined Aug 2006, 1528 posts, RR: 2
Reply 9, posted (1 year 10 months 3 weeks 1 day 20 hours ago) and read 3126 times:

Good Lord. We would fly multiple legs in a 10 or so hour day with the Citation X and never do a quick or full align other than when powering up.

Most days it would take care of itself as we shut the aircraft down during longer turns, but not always.


User currently offlineseven3seven From United States of America, joined Apr 2005, 318 posts, RR: 23
Reply 10, posted (1 year 10 months 3 weeks 1 day 18 hours ago) and read 3088 times:

Thank you KAUSpilot (Eric) for a very nice response. An aircraft sitting unattended for long periods of time is certainly a good reason. As well as the long flight times on your aircraft.

And the RNP 5 requirement in Europe might be the simplest explanation.

Thanks



My views are mine alone and are not that of any of my fellow employees, officers, or directors at my company
User currently offlineBA777 From United Kingdom, joined Jun 2001, 2179 posts, RR: 7
Reply 11, posted (1 year 10 months 3 weeks 1 day 17 hours ago) and read 3067 times:

One full alignment at the start of duty (737NG) and only do a realign if we get the message on the CDU to do so.

User currently offlinesandrozrh From Switzerland, joined Feb 2007, 3428 posts, RR: 50
Reply 12, posted (1 year 10 months 1 week 3 days 11 hours ago) and read 2712 times:

We do quick alignments during turnarounds if the residual groundspeed is less than five knots and if we're staying on the same aircraft for the next sector. In all other cases we will do full alignments. Also, the IRS positions need to be within 5NM from the airports reference position after realignment, or a new, and in this case full, alignment is necessary. This is our procedure on the A32S, A330 and A340 and is Airbus procedure, so im not sure why other European airlines would do otherwise.

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