GPS in air transport

[Malybenek]

I take it that every modern aircraft is fitted with a GPS device these days, yet I can't seem to imagine a situation where such a unit serves as the primary navigation system.

For instance, during the war in Bosnia the military tampered with the GPS system to impede on enemy operations, which rendered many high-tech weekend yachtsmen blind.
I believe this is not an isolated example.
All this does make me wonder whether GPS is reliable enough an invention to become widespread in aviation.

I'd appreciate any help on this matter, particularly from airline pilots:

1. Where and when on commercial flights is GPS used for navigation?
2. Do Fligh Management Systems utilize any GPS inputs?
2. What's your 'onboard' experience with GPS?
3. Are you enthusiastic or rather reluctant?

Thanks for any thoughts.

MB

[reynoldsno1]

The definition of 'primary navigation system' varies from State to State. GPS is not regarded as a 'sole means' navigation system, though I believe there are exceptions to this in remote areas such as Alaska.

1) The USA, Australia, New Zealand and many SW Pacific countries
2) Just about all of them all the time
3) Wonderful - but you shold have an understanding of how it works and its limitations
4) It works, but I can understand the reluctance in Europe as the operating environment is quite different from just about everywhere else.

[Malybenek]

Reynoldsno1, thank you for your reply.

Any thoughts from European pilots then?

[Max Angle]

On our (bmi) Airbus aircraft we have dual GPS units that feed the flight management system along with triple IRS and radio updating. The GPS is the primary means of navigation during all phases of flights except the approach phase when we are back (for the moment) to standard radio aids.

[RadarContact]

For instance, during the war in Bosnia the military tampered with the GPS system to impede on enemy operations, which rendered many high-tech weekend yachtsmen blind.

For this reason, such action would be announced via NOTAM to warn all GPS operating carriers - or should be, at least...

However, the on-board GPS systems, like most other, are equipped with RAIM (receiver autonomous integrity monitoring) which can estimate its position error by using additional satellite input to the required 4 satellites for a position in 3D space.

In case of a deterioration of the GPS signal quality the system would simply be ignored by the FMS - or should be... ;)

[Check 6]

When the U.S. Department of Defense introduces an error into their GPS system, it is done regionally, not worldwide. Also, the error introduced is not that large. I believe that RNP-5 standards can still be me, but please correct me if someone has seen different.

:)

[Otterman]

A few years back the aircraft that I fly (Boeing 747-300) went through a major cockpit upgrade. Our old INS setup was replaced with a triple GPS, triple IRS, triple FMC package. Our analog insturments were replaced by a full EFIS panel. Our IRS's primary function is to provide data to our EADI and our CADC (central air data computers), and their triple mix position is used as back-up navigation mode. Primary navigation is by our triple GPS. In the three years we have been operating in this configuration I have never lost GPS integrity. We have been certified to use the LNAV mode during any non-precision approach down to normal limits. Condition is that we do monitor the navigation aid that the approach is based on. At a few destinations NDB approaches are still made, and it is a thing of beauty to see the LNAV mode do its thing using the GPS's. I started out in htis business in the Arctic shooting stars, and flying grid navigation. The GPS is the next big step forward in commercial aviation. Once we get the VNAV and LNAV properly interfaced the non-precision approach (our biggest killer) will be a thing of the past. I can''t wait. Regards, O.

[Intruder]

I fly 747-400s equipped with GPS. GPS is the primary input to the FMS, and is used as the sole means of FMS navigation as long as at least 1 of the 2 GPS receivers is operating within normal parameters.

The 3 Inertial Reference Units (IRUs) make up an Inertial Reference System (IRS) that continues to provide a secondary FMS position, to which the system can revert immediately upon loss of GPS data. That FMS position is normally updated by DME/VOR/LOC as described by Mike Jenvey.

All 6 positions -- GPS L, GPS R, IRS L, IRS C, IRS R, and IRS(3) [the updated, summed position calculated by the FMS from the IRSs and DME/VOR/LOC updates) can be viewed independently on the FMS CDU and/or Nav display as desired.

GPS works! It gets me around the world without getting lost (or further than about 600' from where I'm "supposed to" be)! Nominal performance (Actual Nav Precision) is 0.06 NM.

[Malybenek]

I'd like to thank all of you for your clear and informative posts.
I have a much better picture mow.

PPRUNE is a wonderful source of information.
Congratulations to those who created this board:) :cool: :)

MB

[123567]

In the South Pacific (where we operate) we are able to use GPS as a sole means navigation system only in oceanic airspace.

Domestic operations can use GPS as a primary means (you must have a "back up" VOR/NDB etc).

The new type IIRS satellites currently being launched will provide even greater accuracy negating the need for systems such as DGPS and WAAS and allowing for precision approaches.