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-   -   GPS users must plan for outages (https://www.pprune.org/tech-log/192057-gps-users-must-plan-outages.html)

Carnage Matey! 3rd October 2005 00:18

Absolutely not, but we fly a fleet of A320s and B744s that are EGPWS but non GPS equipped so clearly it can work without GPS.

UNCTUOUS 3rd October 2005 08:02

Carnal Matey! said


You don't need GPS to use EGPWS. I've flown plenty of aircraft that have EGPWS fitted but not GPS. You just need to make sure you do nav accuracy checks to ensure the FMS/IRS position is within tolerance compared to the raw data position.
Perhaps you should review these two links:

LINK ONE


LINK TWO

Groundloop 3rd October 2005 08:52

"I can count on exactly three times when the GPS signal faded or was not available...and never during an approach to GPS minimums"

So, 411A, let's get this right. You have experienced GPS becoming unavailable - so it is NOT 100% reliable. But because it happened not to be at a critical phase of the flight - it's all right then. Aren't you the lucky one! What if it had occured at a critical phase of the flight?

One major problem with GPS is if one satellite begins to transmit rubbish. This can result in incorrect positions being calculated and may take time to be detected and the satellite switched off or the constellation health message upgraded to broadcast this fact.

That's why there are systems like EGNOS which have fixed receivers at known positions constantly monitoring their GPS derived positions and immediately broadcasting notification of GPS unreliability. If GPS was perfect EGNOS (or WAAS and LAAS) would not be needed.

It's not a "not invented here" syndrome in Europe. It is more of a "it WAS invented here" syndrome in the US and therefore it MUST be perfect. Fact is, it isn't! And where lives could be at risk sticking your head in the sand is not a professional approach.

411A 3rd October 2005 21:08

All very elementary
 
<<So, 411A, let's get this right. You have experienced GPS becoming unavailable - so it is NOT 100% reliable. But because it happened not to be at a critical phase of the flight - it's all right then. Aren't you the lucky one! What if it had occured at a critical phase of the flight?>>

What?
You have never heard of INS becomming unreliable?
I have had two out of three fitted failing more the once certainly, yet we pressed on with the flight, using other modes of navigation.
Just because 'it' might fail enroute, is no reason to get in a panic, now is it?
For approaches, there are VOR's and ILS's available, and indeed the odd diversion might be needed.
All in the name of the game of professional flying.

Now, I can understand why younger guys might have a slight 'problem' but those of us who have been around awhile, manage to cope.
Then we come to map shift on several types just a few short years ago.
Did these guys panic, and have a fit?
I suspect, surely not.

reynoldsno1 3rd October 2005 23:37


One major problem with GPS is if one satellite begins to transmit rubbish. This can result in incorrect positions being calculated and may take time to be detected and the satellite switched off or the constellation health message upgraded to broadcast this fact.
Which is precisely why IFR certificated aircraft receivers have their own integrity monitoring and warning ssytems... and why those States experienced in the use of GPS have developed and implemented technical, training, regulatory and operational procedures to ensure safety of flight......

UNCTUOUS 5th October 2005 03:33

First Modernized GPS Satellite Launched
 
The first modernized GPS satellite meant to provide significantly improved navigation performance for civilian users worldwide, and U.S. military for its special purposes, has been put into orbit.

The satellite is the first in a series of eight GPS IIR-M satellites that will offer a variety of improvements for GPS users' once initial operational capability is reached. This latest series will offer a variety of enhanced features for GPS users, such as a new antenna panel that provides increased signal power to receivers on the ground, two new military signals for improved accuracy, enhanced encryption and anti-jamming capabilities, and a second civil signal that will provide non-military users with an open access signal on a different frequency that should improve its capability for critical navigation purposes.

The current GPS constellation of 28 spacecraft includes 12 fully operational Block IIR satellites, which were previously developed to improve the global coverage and overall performance of the system.

The dash M satellite, built by Lockheed Martin for the U.S. Air Force contingent at the Navstar GPS Joint Program Office, was launched aboard a Delta II rocket on September 25 from Cape Canaveral in Florida. 10-02-2005.

pantyripper 5th October 2005 05:08

My 2 cents worth....Try using the damm thing in my neck of the woods and you might change your ideas on GPS reliability. We fly GPS NPA into a field with no other aids and have failures on a regular basis, lucky for me the other side kept working, but we do have times when both sides fail, luckily in VMC though. But still my company insists that it's nothing to be worried about, especially the high terrain ....which they say is depicted on the EHSI via the TAAD of EGPWS, .....I guess not. God knows how we got approved to do the approach?:}

OzExpat 5th October 2005 07:16


God knows how we got approved to do the approach?
I'm not God, but I'll take a wild guess at the answer to that. It probably had a bit to do with training, certification, maybe even some periodic proficiency checks, and procedures in your Ops Manual that talk about action in the event of non-availability of GPS.

If that isn't enough and if, as I suspect, you're in Oz and using TSO C129a gear, then you need an alternate that has a serviceable navaid. But then, I'm sure you knew all of that already. :}


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