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INS Dead-reckoning. Does It Still Happen Often?  
User currently offlinethenoflyzone From Canada, joined Jan 2001, 2493 posts, RR: 11
Posted (11 months 1 week 1 day 9 hours ago) and read 7659 times:

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]


us Air Traffic Controllers have a good record, we haven't left one up there yet !!
14 replies: All unread, jump to last
 
User currently offlinethenoflyzone From Canada, joined Jan 2001, 2493 posts, RR: 11
Reply 1, posted (11 months 1 week 1 day 4 hours ago) and read 7522 times:

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]


us Air Traffic Controllers have a good record, we haven't left one up there yet !!
User currently offlinelonghauler From Canada, joined Mar 2004, 4990 posts, RR: 42
Reply 2, posted (11 months 1 week 1 day 3 hours ago) and read 7483 times:

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.



Never gonna grow up, never gonna slow down .... Barefoot Blue Jean Night
User currently offlineAR385 From Mexico, joined Nov 2003, 6214 posts, RR: 30
Reply 3, posted (11 months 6 days 11 hours ago) and read 7078 times:
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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?



MGGS
User currently offlineBMI727 From United States of America, joined Feb 2009, 15744 posts, RR: 27
Reply 4, posted (11 months 6 days 7 hours ago) and read 6999 times:

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.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlinePihero From France, joined Jan 2005, 4448 posts, RR: 76
Reply 5, posted (11 months 6 days 7 hours ago) and read 6993 times:
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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 ).



Contrail designer
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17040 posts, RR: 66
Reply 6, posted (11 months 6 days 3 hours ago) and read 6910 times:

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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMax Q From United States of America, joined May 2001, 4524 posts, RR: 18
Reply 7, posted (11 months 5 days 23 hours ago) and read 6847 times:

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.



The best contribution to safety is a competent Pilot.
User currently offlineBMI727 From United States of America, joined Feb 2009, 15744 posts, RR: 27
Reply 8, posted (11 months 5 days 22 hours ago) and read 6832 times:

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?



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineAR385 From Mexico, joined Nov 2003, 6214 posts, RR: 30
Reply 9, posted (11 months 5 days 22 hours ago) and read 6823 times:
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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.



MGGS
User currently offlinePihero From France, joined Jan 2005, 4448 posts, RR: 76
Reply 10, posted (11 months 5 days 19 hours ago) and read 6779 times:
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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 )



Contrail designer
User currently offlineFlighty From United States of America, joined Apr 2007, 8544 posts, RR: 2
Reply 11, posted (11 months 3 days 15 hours ago) and read 6354 times:

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

User currently offlinePihero From France, joined Jan 2005, 4448 posts, RR: 76
Reply 12, posted (11 months 3 days 15 hours ago) and read 6338 times:
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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]


Contrail designer
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17040 posts, RR: 66
Reply 13, posted (11 months 3 days 14 hours ago) and read 6331 times:

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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineapodino From United States of America, joined Apr 2005, 4280 posts, RR: 6
Reply 14, posted (11 months 1 day 5 hours ago) and read 5981 times:

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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