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Airliners Still Use INS?

Mon Oct 13, 2003 10:39 pm


According to some theories, the unfortunate KE 007 shootdown was caused by the fact the pilot of the plane did not program the inertial navigation system (INS) properly, which resulted in the plane going off-course and into Soviet territory on its flight from ANC to SEL in 1983.

With today's GPS (and after 2008, Galileo) satellite navigation systems (which has accuracy around 10 meters), do airliners still need to program the INS system while the plane is on the ground? Or is INS replaced by systems that work by receiving satellite navigation signals?
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RE: Airliners Still Use INS?

Mon Oct 13, 2003 11:08 pm

Yes airliners still need to program a position into the INS. Ironically on some aircraft all you have to do is take the GPS position and punch it into the INS.
Never take financial advice from co-workers.
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RE: Airliners Still Use INS?

Tue Oct 14, 2003 3:13 am

a) GPS has its limitations - notably on polar routes. Galileo is supposed to alleviate those, but we´re not there, yet.

b) You need to have a backup in case GPS reception (or even transmission!) should fail.

RE: Airliners Still Use INS?

Tue Oct 14, 2003 4:37 am

The Classic 747s sure still have INS...
The airplanes I presently fly are equipped with 3 INS (which are operated in "triple mix") - and we have 2 GPS to update #1 and #2 INS... By triple mixing it also updates the #3 INS... We also have DME update capability.
All that gives us maximum accuracy for RNP-5 operations (MNPS)...
Happy contrails  Smile
(s) Skipper
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RE: Airliners Still Use INS?

Tue Oct 14, 2003 5:11 am

You can think of it this way.

The main advantage of the Inertial Navigation System, or INS, is simply that it's internal...fully contained in the aircraft. One disadvantage is that on average, it loses accuracy at the rate of about one nautical mile per hour.

The main advantage of GPS is of course its accuracy. GPS signals for civilian use, however, are very weak....extremely weak, in fact....and may provide inadequate reception and with loss of RAIM can be error-prone in some areas.

So GPS in a transport-category airplane that's equipped with an INS type system periodically updates the INS, thereby producing the "best of both worlds" so to speak.
I got my head checked--by a jumbo jet
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RE: Airliners Still Use INS?

Tue Oct 14, 2003 6:27 am

Qantas 747-400s use three IRS (Inertial Reference Systems, not the tax man) updated with VOR/DME and two onboard GPS.
The 767s use three IRS updated with VOR/DME, with several aircraft equipped with GPS.
The 747-300s use three INS, however they are now being updated with IRS and GPS as part of a refit.
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RE: Airliners Still Use INS?

Tue Oct 14, 2003 1:33 pm

As has already been mentioned INS is completely self contained, which is a good thing.

What good is having 2 or 3 GPS systems if they all run off the same satellites?

RE: Airliners Still Use INS?

Tue Oct 14, 2003 1:53 pm

Dear L-188 -
With 2 GPS - you can continue with one GPS remaining if second fails, the one unit will provide sufficient update, to the INS in "T-Mix"... Our current configuration still gives full flexibility, i.e. in cas of one INS on MEL... It was the least inexpensive upgrade, using these LTN-92 type INS systems. Remember, DME update requires DME stations... not too many right in the middle of the oceans...
Happy contrails -
(s) Skipper
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RE: Airliners Still Use INS?

Wed Oct 15, 2003 11:28 am

If my memory serves me correctly, KAL 007 INSs were programmed correctly but they left the Navigation mode select switch in HDG position instead of INS position. So basically INS were not given the task of navigating. It was not an INS error but a pilot error.

I am not familiar with the latest generation aircrafts but I suspect that even on today's most sophiticated aircrafts same mistake can happen , But track deviation alert and warnings are better, I am sure.
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RE: Airliners Still Use INS?

Wed Oct 15, 2003 11:53 am

The most plausible theory behind KAL 007 is the INS being left in HDG mode. Unfortunately the FDR and CVR were never recovered by the NTSB so they'll never be 100% sure.
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RE: Airliners Still Use INS?

Wed Oct 15, 2003 12:24 pm

Skipper believe it or not but there are dead spots on the north side of the Brooks range of Alaska where you can't pick up the three satillites you need for navigation.

I am sure that it is the same at other polar locations.

RE: Airliners Still Use INS?

Wed Oct 15, 2003 2:13 pm

Dear L-188 -
Very well aware of "dead spots" in Polar areas - but if we lost the update capability (from GPS) for 1 hour or 2... the INS in T-Mix keep sufficient accuracy to even be called capable of MNPS (RNP-5)... no problems in case that happens...
Happy contrails  Smile
(s) Skipper
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RE: Airliners Still Use INS?

Thu Oct 16, 2003 6:11 am

The KAL flight was flying a direct routing, one done on many occasions. This time they got caught. Couple the practice with the hot-headed MIG pilot and history was made.

No secret with this episode.

Re: the question asked - lots of modern day airliners use INS as secondary nav in BRNAV airspace and primary in "IRS NAV ONLY" airspace.

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