IRS Alignment

[Goldenrivett]

Originally Posted by Blacksheep

If the Inertial reference System loses its position in flight it is seriously unserviceable, so why would you want to realign it?

Hi Blacksheep, enjoy: Laseref VI. I did.

[gums]

Salute!

Thank you, Rivett a really neat system, and

With a few operating instructions, many requirements and such will be answered for the folks here

I now step off the platform.

Gums sends..

[BizJetJock]

Interesting that the Honeywell document claims the Laseref VI is installed in the Challenger 605, while the FCOM states the Laseref V. It may be that the production standard was upgraded and the text about realignmnet conditions was changed, but the intro text wasn't. And unless the change was pre-production then there should be text covering both variants.
Ah, well, not the first error i've come across in an aircraft manual.

[Blacksheep]

Hi Blacksheep, enjoy: Laseref VI. I did.

So did I. It confirmed that GPS input is required for 'Align in Motion' to work. There's a world of difference between detecting aircraft attitude and not being temporarily unsure of location.

[flash8]

We used to do full alignments on the 737 Classic every stop, until the IRS failure rate started climbing, we were then told to fast align (pre RVSM) which seemed to clear the issues. IRS realignment in flight I was always under the impression is impossible... I actually laughed at somebody who thought it could be done... but I guess technology has progressed...

[gums]

.Salute!
It may surprise you, Flash, but a year or two before you were born we could do an airborne alignment in our SLUF.

Crude level for the "platform" like most AHRS did those days, then use a rough present position to start the alignment ( that provided theoretical Earth rotation data) and then use velocity inputs from our doppler. Find a good reference for a position update 15 or 20 minuites later and walla!

As you assert, technology has progressed, and further and faster than most of us ever imagined.

Gums sends...

[flash8]

It may surprise you, Flash, but a year or two before you were born we could do an airborne alignment in our SLUF.

Gums, thank you for this, you live and learn!

[Turbavykas]

I think theoretically it's possible but IRS is an independent system and quite old on older aircrafts with simple cpu so just to make it simpler and save cost it's done this way. It will make no sense to depart unaligned anyway because artificial horizont will not work.

[EEngr]

Originally Posted by flash8

IRS realignment in flight I was always under the impression is impossible...

Probably true for commercial aircraft. In theory it can be done. GPS can correct for IRS position errors, but not so much for attitude. There are GPS receivers that employ multiple antennas (on wingtips and tail) that can compute 'which way is up' based on comparing the phase of a received satellite signal at each. But I'm not sure how precise that will be.

Back in the 1960s, gyro IRS systems that were expected to remain precise over longer periods of time could use star spotter systems to provide in-flight calibration. Apollo had a manually operated system on board the command module. And the B-70 design was to incorporate an automated system that would work at high altitudes even in daylight.

[Broomstick Flier]

IIRC, the SR-71 had such an astronavigation system installed and fully operational

Quick edit: Indeed it had it. It was the Nordtronics NAS-14.
https://timeandnavigation.si.edu/mul...igation-system

BF

[jmmoric]

Now it's been stated that the GNSS systems can update the IRS/INS.

But what about DME/DME or VOR/DME, in case the GNSS is being "offset" or is unavailable... or will the system stay on the IRS/INS until an update is commanded, and then use the groundbased stations for updating reference?

Or is the FMS constantly checking IRS/INS versus all other sensors?

Edit: RNAV