Topic Author
Posts: 1960
Joined: Tue Feb 06, 2001 5:56 pm

Requesting Help With Navigation Systems

Sat Mar 16, 2002 4:32 am

Hey all, I could use some information of some less-known navigation systems:

1) Is this system still in use?
2) If so, whats its precision, whats it used for, what onboard devices are used for it?

1) Whats the 'development status' of MLS? Will it be applied in the near future?

LORAN (any):

INS (or IRS):
1) Whats the average error per flight hour on state-of-the-art INS
2) is it certified to be used as 'sole means of navigation' for airliners?

ILS CAT-IIIc approach
1) How does the pilot stay on the runway centerline after touchdown and ILS signal loss if visibility is 0-0? Is there any additional transmitter, or does any ILS antenna have a BC signal which is usable for taxiing?

I'd really appreciate any additional operational information on those system, also what other not-well-known nav systems are used in civil aviation today (not ILS, VOR, NDB or GPS)

Posts: 93
Joined: Thu Feb 07, 2002 5:58 pm

RE: Requesting Help With Navigation Systems

Sat Mar 16, 2002 6:17 am

OMEGA was decomissioned a few years ago.

(As far as I know)MLS once held great promise but has since fallen by the wayside.

IRS (or ADIRS in the Airbus world) On the 330 with three ADIRS and solely navigating with the ADIRS the Estimated Position Error is +8nm/h for the first 21 minutes and +2nm/h after that. I would suggest that unless there was a problem these limits would NEVER be approached.
Triple ADIRS are great for crossing oceans. Once you get within range of VOR's and NDB's again the ADIRS are all automatically updated to the exact postion and the airplane will correct it's course.

On a CAT III approach the airplane maintains the centerline following the autoland. If the transmitter drops off line there is a back-up that should provide continous transmission.
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Joined: Sun Sep 30, 2001 5:39 am

RE: Requesting Help With Navigation Systems

Sat Mar 16, 2002 9:04 am

Well I am not sure what its accuracy in the air, Loran C has an accuracy of 1nm in most marine cases.
At worst, you screw up and die.
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Joined: Tue Jan 01, 2002 1:21 am

RE: Requesting Help With Navigation Systems

Sat Mar 16, 2002 9:34 am

There are 2 possibilities for holding the centerline in 0-0 operations that can even be done manually. The first is to hold the localizer centered on roll-out and the second, should the localizer be lost, is to hold the exact runway heading. This method goes back as far as WWII.
The real difficulty comes after leaving the runway; hence the "Follow Me" vehicles you sometimes see.
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RE: Requesting Help With Navigation Systems

Mon Mar 18, 2002 4:50 am

MLS to my knowledge was a military endeveor, I think they still use it today, but unsure. It like ILS, but uses microwave.
Ziggy  Confused

Topic Author
Posts: 1960
Joined: Tue Feb 06, 2001 5:56 pm

RE: Requesting Help With Navigation Systems

Tue Mar 19, 2002 5:23 am

Thanks guys, it helped me out  Big thumbs up


RE: Requesting Help With Navigation Systems

Tue Mar 19, 2002 6:49 am

Sorry for the late response. I've been away a while.
The Omega had a range of about 8000nm. Its accuracy was about 5000ft.

Loran-C had a range of about 1200nm with accuracy from 100 ft to 1200ft, depending on range. Loran-C is still being used by ships, not sure if there's any airborne use anymore (not on airliners anyways).

The INS can be used as sole means for RNP-10 airspace (for up to 12.5 hours).

MLS for commercial aviation is no more. The FAA abandoned it long ago. The future implementation is LAAS.

The Localizer beam is used on the ground (during rollout and takeoff) to maintain centerline.

Hope this helps. Best Regards,
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RE: Requesting Help With Navigation Systems

Sun Mar 24, 2002 5:30 am


We used OMEGA nav on our Boeing 727-2M7's out of Guam. The navigation is ground based, low frequency. The unit will pick up a minumum of 3 stations, and triangulate the aircraft's position. Accuracy was fair. It frequently would go into DEAD RECONING the instant the airplane poked it's nose into a cloud.

We had two sets on board. The challenge when leaving Seoul (Korea) for Guam was to get an update when passing over known navigational facilities. We would usually do this at Ikeshima, on the north west coast of Honshu, and then again after passing the last land position at a DME fix off of the final VOR station. Sometime along the route, it was normal for one of the two units to begin telling us bad information. The question was, "which one?" We could get an accurate fix off the Iwo Jima TACAN with bearings off of the Anderson NDB on Guam and the IWO NDB.

These were nice units when they worked... by Tracor our of Mojave, CA. A $35,000 card would convert the unti to SATNAV... but the company figured they paid us to do the navigating, and they were right. It's an OK system.

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