737NG - IRS

[B737NG_Pilot]

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.

[ImbracableCrunk]

My airline turns the IRS off on the shutdown.

[de facto]

So why don't we turn off the IRS during the shutdown procedure?

You tell us:}

[B737NG_Pilot]

I don't know. I feel there is a reduction in the life span of the IRS. Every time we turn it off.

[RAT 5]

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.

[PPRuNeUser0190]

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.

[Denti]

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.

[Skyjob]

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.

[RAT 5]

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.

[BOAC]

It is not unknown to switch it on in the morning and off in the evening and that is all!

[Avenger]

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"

[B737NG_Pilot]

Yesterday I flew, 3 sectors without aligning IRS even once. Its only in the fourth sector I recevied IRS POS/ORIGIN DISAGREE. A/C had Dual FMC with GPS updates on.

[stilton]

I've aligned at the gate in some very strong winds, that has never been an issue.

[RAT 5]

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.

[stilton]

Interesting R5, have never seen that but I can see how with your description.

Best wishes.

[737ngpilot]

Full align on my property, except when windy

[vapilot2004]

Short sector flights = fast align.
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.

Nail on the head right here, SJ.

[FlyingStone]

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.

Even a quick re-align will reset GS from those couple of knots on the ground to 0.

We do a full align on each sector (non-GPS classic).

[BOAC]

Even a quick re-align will reset GS from those couple of knots on the ground to 0. - correct but not relevant! It is platform alignment that is corrected by a full align whereas a rapid merely, as you say, zeroes the residual speed.