737NG - IRS
Thread Starter
Joined: Mar 2013
Posts: 177
Likes: 0
From: 36,000'
737NG - IRS
As per the preliminary pre-flight procedure, the IRS's must be re-aligned completely before each flight.
So why don't we turn off the IRS during the shutdown procedure? I mean for a crew change during, each flight day, they have re-align the IRS anyways completely.
Also the secure is done, only on the last flight of the day, where we turn the IRS's off.
So why don't we turn off the IRS during the shutdown procedure? I mean for a crew change during, each flight day, they have re-align the IRS anyways completely.
Also the secure is done, only on the last flight of the day, where we turn the IRS's off.
Joined: Jun 2000
Posts: 4,507
Likes: 4
From: last time I looked I was still here.
Fully realigning the IRS every flight is a company procedure; perhaps. For Boeing a 'fast realign' is enough, especially with GPS a/c. The B757 I assume had similar systems to B733 classics. We used to fast align on turn-rounds in Europe, but a full align before any ETOPS or long over water flight. On NG we sued to fast align on turn-rounds and full align on crew change because the a/c was shutdown, or it's nice to start with a clean sheet of paper if the crew are at the steps.
Joined: Sep 2008
Posts: 61
Likes: 0
It is Boeing procedure to reset the IRS's. The preliminary needs to be done before each flight and the first step is:
IRS........OFF, then NAV
if your company says that it needs to be done only once per day, then it is a company procedure.
IRS........OFF, then NAV
if your company says that it needs to be done only once per day, then it is a company procedure.
Joined: Mar 2001
Posts: 4,562
Likes: 33
From: I wouldn't know.
We use the same procedure in my current company, completely off and then to NAV again for each flight. In my previous company we just did a quick realign and used to do that on the classics (where we didn't have GPS updating) as well.
To be honest when i was taught that difference i just shrugged and did it that way, not a big issue at all, just a difference in technique, both ways work.
To be honest when i was taught that difference i just shrugged and did it that way, not a big issue at all, just a difference in technique, both ways work.
Joined: Jan 2000
Posts: 860
Likes: 0
From: FL410
Next time after a flight have a look at your POS as indicated on screen and in FMC.
If any of the positions indicate a small but significant shift from the GPS known GATE/PARKING position then do a FAST realign.
If any of the positions indicate a large shift from known position, execute a FULL align to get rig of nonexistent ground speed which will be displayed on FMC pages whilst parked.
If any of the positions indicate a small but significant shift from the GPS known GATE/PARKING position then do a FAST realign.
If any of the positions indicate a large shift from known position, execute a FULL align to get rig of nonexistent ground speed which will be displayed on FMC pages whilst parked.
Joined: Jun 2000
Posts: 4,507
Likes: 4
From: last time I looked I was still here.
It is Boeing procedure to reset the IRS's.
I flew for airlines that did full align at crew changes and fast align on same crew turn-rounds. Boeing designed the fats align feature, so we used it. I then flew for an EU airline that full aligned every sector. After a few years there was a Boeing audit and the TC asked why we did that. It changed to the former procedure at Boeing's advice. So, there are 2 methods to reset an IRS.
I flew for airlines that did full align at crew changes and fast align on same crew turn-rounds. Boeing designed the fats align feature, so we used it. I then flew for an EU airline that full aligned every sector. After a few years there was a Boeing audit and the TC asked why we did that. It changed to the former procedure at Boeing's advice. So, there are 2 methods to reset an IRS.
Joined: Nov 2000
Posts: 624
Likes: 0
From: I wish I knew
If the IRS(s) are aligned and there are 2 FMCs the aircraft can fly for up to 6 hrs without the ref to conventional nav aids, should you land in windy city it may be impossible to align the IRS with the airframe moving around, hence it may be better not to attempt. We align " as required"
Joined: Jun 2000
Posts: 4,507
Likes: 4
From: last time I looked I was still here.
Flying for the airline who insisted on full align every sector I did so in 40kt winds. At the gate R IRS would not align; a/c was rocking. Loaded up and taxied out and set up a/c // with the wind. It still would not align.
Thankfully, later on, they saw sense and used fast align, and non at all in strong winds.
Thankfully, later on, they saw sense and used fast align, and non at all in strong winds.
Joined: Aug 2005
Posts: 1,693
Likes: 0
From: fairly close to the colonial capitol
Short sector flights = fast align.
Longer sector (3+hours) = full alignment.
Drift is the reason.
Nail on the head right here, SJ.
Longer sector (3+hours) = full alignment.
Drift is the reason.
Next time after a flight have a look at your POS as indicated on screen and in FMC.
If any of the positions indicate a small but significant shift from the GPS known GATE/PARKING position then do a FAST realign.
If any of the positions indicate a large shift from known position, execute a FULL align to get rig of nonexistent ground speed which will be displayed on FMC pages whilst parked.
If any of the positions indicate a small but significant shift from the GPS known GATE/PARKING position then do a FAST realign.
If any of the positions indicate a large shift from known position, execute a FULL align to get rig of nonexistent ground speed which will be displayed on FMC pages whilst parked.
Joined: Apr 2010
Posts: 1,319
Likes: 100
From: IRS NAV ONLY
Originally Posted by skyjob
If any of the positions indicate a large shift from known position, execute a FULL align to get rig of nonexistent ground speed which will be displayed on FMC pages whilst parked.
We do a full align on each sector (non-GPS classic).
Per Ardua ad Astraeus
Joined: Mar 2000
Posts: 18,575
Likes: 4
From: UK
Originally Posted by FlyingStone
Even a quick re-align will reset GS from those couple of knots on the ground to 0.
