Thenoflyzone
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INS Dead-reckoning. Does It Still Happen Often?

Thu Oct 17, 2013 7:50 pm

AC still has quite a few A319s, A320s and B763s with no GPS, just INS. Must be the same thing with some of the legacy carriers like DL or UA across the border.

Now, when over the Caribbean or even the Atlantic, are there any routes in particular where the aircraft is out of range of DMEs or VOR's in order to update its position? If so, where and for how long.

I'm thinking maybe somewhere south of Bermuda, on a YYZ- BGI run perhaps, or YYT-LHR, or even on a YYZ-MAD 767 run, crossing the Atlantic slightly more south than other flights, thus being further from the DMEs and VORs of Greenland and Iceland

Thenoflyzone

[Edited 2013-10-17 13:55:15]
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Thenoflyzone
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RE: INS Dead-reckoning. Does It Still Happen Often?

Fri Oct 18, 2013 1:05 am

Spoke with an AC A319 pilot today, and he told me that YYT-LHR is always operated by a GPS equipped A319.
Had a look on flightradar24.com, and yes, AC822 is always operated by C-GITR or C-GITP, the two latest A319s in AC's fleet.

http://www.flightradar24.com/data/flights/ac822

I'm guessing it's the same for flights going deep into the Caribbean as well.

Thenoflyzone

[Edited 2013-10-17 18:09:29]
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longhauler
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RE: INS Dead-reckoning. Does It Still Happen Often?

Fri Oct 18, 2013 2:03 am

No AC aircraft have INS. The last was the L1011.

The older (non GPS equipped) A319s and A320s have IRS, and with updates they are pretty reliable (within 0.3 miles). Without updates, namely when flying to the Caribbean, they can be up to a mile off course when updates are available again. This complies with all required navigation capability.

The older A319s and A320s are in the process of being updated with GPS, about half are done. This is not for long range navigation, as they already comply, but for GPS/GNSS approach capability.

Quoting thenoflyzone (Reply 1):
C-GITR or C-GITP, the two latest A319s in AC's fleet.

This was not for navigation capability, but for the uprated engines and performance. Those two A319s are heavier than the rest in the fleet.
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AR385
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RE: INS Dead-reckoning. Does It Still Happen Often?

Sat Oct 19, 2013 5:52 pm

Quoting thenoflyzone (Thread starter):
Now, when over the Caribbean or even the Atlantic, are there any routes in particular where the aircraft is out of range of DMEs or VOR's in order to update its position? If so, where and for how long.

I´m confused. Why does the INS need VORs or DMEs to update its position? I thought there was a database of coordinates the crew inputs at the gate in a complicated procedure. After that that´s it. Or am I wrong?
 
BMI727
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RE: INS Dead-reckoning. Does It Still Happen Often?

Sat Oct 19, 2013 9:26 pm

Quoting AR385 (Reply 3):
Why does the INS need VORs or DMEs to update its position? I thought there was a database of coordinates the crew inputs at the gate in a complicated procedure.

Inertial navigation systems drift over time and need periodic updates based on known locations.
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Pihero
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RE: INS Dead-reckoning. Does It Still Happen Often?

Sat Oct 19, 2013 9:47 pm

Quoting AR385 (Reply 3):
Why does the INS need VORs or DMEs to update its position?

Because with time the INS position drifts and accuracy is degraded on each platform.
Even on GPS-equipped airplanes, the IRS platforms are updated by DME / DME, VOR / DME or even LOC , on its own or with DME / DME / LOC or VOR / DME / LOC.
Without GPS, these different updating combinations determine a class of RNP ( required Nav precision ).
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Starlionblue
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RE: INS Dead-reckoning. Does It Still Happen Often?

Sun Oct 20, 2013 1:29 am

Quoting AR385 (Reply 3):
I thought there was a database of coordinates the crew inputs at the gate in a complicated procedure. After that that´s it. Or am I wrong?

It's not that complicated really. The gate/parking space has a known position which is input into the system before moving. Platform alignment takes 5-20 minutes, depending on latitude and type/age of the platform.

As mentioned, the system then uses radio location (most precise is DME/DME) to correct for drift. So after an oceanic passage with no VORs in range, you can get a correction of several miles as you're in range again, and the plane turns. Then again with GPS such corrections are becoming things of the past.

This is all transparent to the pilots, as navaids are tuned and selected automatically by the system, and position is also updated automatically.
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Max Q
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RE: INS Dead-reckoning. Does It Still Happen Often?

Sun Oct 20, 2013 5:35 am

Quoting AR385 (Reply 3):

I´m confused. Why does the INS need VORs or DMEs to update its position? I thought there was a database of coordinates the crew inputs at the gate in a complicated procedure. After that that´s it. Or am I wrong?

You are thinking along the right lines but we don't even do that anymore, we input the GPS co-ordinates (after checking they are correct ) to the IRS at the gate.
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BMI727
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RE: INS Dead-reckoning. Does It Still Happen Often?

Sun Oct 20, 2013 6:24 am

Quoting Max Q (Reply 7):
You are thinking along the right lines but we don't even do that anymore, we input the GPS co-ordinates (after checking they are correct ) to the IRS at the gate.

Can you use GPS to update the IRS in flight?
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AR385
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RE: INS Dead-reckoning. Does It Still Happen Often?

Sun Oct 20, 2013 6:55 am

Quoting BMI727 (Reply 4):
Inertial navigation systems drift over time and need periodic updates based on known locations.
Quoting Pihero (Reply 5):
Because with time the INS position drifts and accuracy is degraded on each platform.
Quoting Starlionblue (Reply 6):
It's not that complicated really. The gate/parking space has a known position which is input into the system before moving. Platform alignment takes 5-20 minutes, depending on latitude and type/age of the platform.
Quoting Max Q (Reply 7):
You are thinking along the right lines but we don't even do that anymore, we input the GPS co-ordinates (after checking they are correct ) to the IRS at the gate.

Thank you all of you. It´s nice to learn something new everyday and to have a forum to go to where people actually take the time to explain things.
 
Pihero
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RE: INS Dead-reckoning. Does It Still Happen Often?

Sun Oct 20, 2013 9:58 am

Quoting BMI727 (Reply 8):
Can you use GPS to update the IRS in flight?

No. It would defeat the redundancy and dispatch reliability of the navigation system...
... but : each IRS computes a *hybrid* position made of INS and GPS , called GPIRS, which is the basis for validating the GPS position... GPIRS is then fed to the FMS...
In flight, the FMS position is - basically - the GPS position.

( A very simplistic explanation )
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Flighty
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RE: INS Dead-reckoning. Does It Still Happen Often?

Tue Oct 22, 2013 1:21 pm

Wonder if they would have improved INS using digital (solid state?) gyros? In any case, old inertial guidance systems are so impressive.
 
Pihero
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RE: INS Dead-reckoning. Does It Still Happen Often?

Tue Oct 22, 2013 2:10 pm

Quoting Flighty (Reply 11):
Wonder if they would have improved INS using digital (solid state?) gyros? In any case, old inertial guidance systems are so impressive.

Already done : Mechanical gyroscopes disappeared from new airplanes in the mid-eighties.
Nowadays, the technology is about *ring laser gyros* which do not have - strictly speaking - any moving parts ; these are the basis of the inertial part of the ADIRS - air data / inertial reference systems - that we have on-board all airliners.
The ADIRS outputs are also digital.
Comparing the precision of laser vs mechanical gyros, the drifts are - ballpark figures - 2nm / hour for the mechanical platform vs .5 nm / hour for the modern IRS... quite a progress !

PS : As in the old days of the INS, each panel was provided data from its own side INS, the flight directors would reflect the difference in the drift of both platforms : the PM side FD would not in general be centered, as in this picture :
View Large View Medium
Click here for bigger photo!

Photo © F-ILIP


Guess who is PF ?
that meant monitoring very often the validity of each platform output... heavy workload !

[Edited 2013-10-22 07:53:32]
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Starlionblue
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RE: INS Dead-reckoning. Does It Still Happen Often?

Tue Oct 22, 2013 2:30 pm

Quoting Flighty (Reply 11):
Wonder if they would have improved INS using digital (solid state?) gyros? In any case, old inertial guidance systems are so impressive.

As Pihero says, mechanical gyros are a thing of the past. Even Cessnas have solid state gyros nowadays.
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apodino
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RE: INS Dead-reckoning. Does It Still Happen Often?

Thu Oct 24, 2013 11:41 pm

Quoting thenoflyzone (Reply 1):
Spoke with an AC A319 pilot today, and he told me that YYT-LHR is always operated by a GPS equipped A319.
Had a look on flightradar24.com, and yes, AC822 is always operated by C-GITR or C-GITP, the two latest A319s in AC's fleet.

Justplanes.com has an excellent Blu-Ray DVD out which shows the operations of these AC in ETOPS very well. It is 30 USD and I highly recommend it.

That being said...I don't know how many planes are actually strictly IRS in a non radio environment anymore. I think most of the airplanes have been converted over to GPS, but I don't know that off the top of my head.

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