757/767 GNSS vs IRU

[mrtango]

Hi folks! So...

Do operators of the 757/767 (UPS/Delta/American/United/BA etc...) have GNSS equipment installed, or are these operators predominantly conducting primary navigation solely using DME/DME/IRU for the FMS?

Would be nice to know, appreciate any insight on this.

[brakedwell]

When I flew the 757 and 767 from 1983 to 1994 - the FMS was updated by DME/DME/IRS.

[mrtango]

Appreciate the response. But...

Certainly position updating was accomplished through DME/DME/IRU at that time. But, the real question is, how many fleets are operating this way without GNSS still today? UPS, for example, is one of the largest 757/767 freight operators, I can only wonder how many of these, if any, are GNSS equipped.

[aterpster]

mrtango,

Do operators of the 757/767 (UPS/Delta/American/United/BA etc...) have GNSS equipment installed, or are these operators predominantly conducting primary navigation solely using DME/DME/IRU for the FMS?

Would be nice to know, appreciate any insight on this

The 757/767 airframe was certified circa 1980.

Circa early to mid 1990s Boeing undated production aircraft to a far more robust FMS, with GPS sensing. But, operators did not retrofit. The price would have been prohibitive.

So, most of the airlines operate 757/767 aircraft with both the original and the highly updated FMS suite, depending upon delivery date.

[aa73]

The GNSS (GPS) FMC on the 75/76 is called Pegasus, and as someone else noted, was introduced in the mid 90s.

I can't speak for other airlines, but as of today, AA's 75/76s are about half Pegasus and half Basic (IRU/DME). However, there is a time frame - I'm not sure of the exact date - where IRU navigation will become obsolete, and everyone must transition to GPS.

AA has been installing the Flat Panel Display System on our 75/76 fleet, which looks much like the 777 panels (albeit a much cheaper version).. and along with that, they are replacing the Basic FMCs with Pegasus.

Any 75/76 that AA received past 1998 or so came new with Pegasus FMC already installed.

[blue up]

Thomson operate mostly old fit 757s with maybe 25% Pegasus. It is the other way round with the 767s, so, a 50:50 split in total.

[grounded27]

there is a time frame - I'm not sure of the exact date - where IRU navigation will become obsolete, and everyone must transition to GPS.

Scarry thought, GNS/gps failures are more common than IRU. I would immagine a single IRU will still be required for a very long time. I believe we will maintain inirtial data (needed anyways for platform) as a backup system for a long time.

[aterpster]

aa73:

I can't speak for other airlines, but as of today, AA's 75/76s are about half Pegasus and half Basic (IRU/DME). However, there is a time frame - I'm not sure of the exact date - where IRU navigation will become obsolete, and everyone must transition to GPS.

Don't know where you heard that one. RNP AR of less than 0.30 or missed approach of less than 1.0 requires at least one IRU.

[mrtango]

Great responses.

Here's another issue. How are the GNSS units augmented for Boeing? I know the FAA has a TSO regarding 5 satellites with RAIM, or 4 if the GPS has baro-aiding. Is there anything that allows GPS augmentation using DME/DME/IRU through the FMS? And, if not, then how is augmentation accomplished?

[FlightPathOBN]

this thread is a mix and match....

RNP approaches are designed with a backup IRU and drift calculations. If you loose GPS integrity, the IRU takes over, and the respective drift rate is used for containment widths.

For vertical, currently RNP uses baro for vnav or it some cases rad alt.

in regards to UPS, they have one of the more substantial RNP capable fleets operating in the US...

[aa73]

Don't know where you heard that one. RNP AR of less than 0.30 or missed approach of less than 1.0 requires at least one IRU.

maybe I'm mistaken, but that was the reason I was given when I asked why they were in such a rush to install GPS... Maybe what they meant was that IRU would only be there for backup, and GPS is the primary means of navigation.

[engfireleft]

I can't speak for other airlines, but as of today, AA's 75/76s are about half Pegasus and half Basic (IRU/DME). However, there is a time frame - I'm not sure of the exact date - where IRU navigation will become obsolete, and everyone must transition to GPS.

That date is January 1st, 2020 when ADS-B becomes mandatory from liftoff to touchdown at major airports and class A and B airspace in the US. The accuracy requirements are such that WAAS or dual frequency GPS's will be the only navigation systems capable besides all the datalink reporting requirements.