Topic Author
Posts: 706
Joined: Wed Aug 25, 2004 5:07 pm

Pacific Routes

Tue Dec 15, 1998 1:58 pm

I have this big question in my head on how the
airlines such as Qantas,AOM,Air Pacific and Air
New Zeland navigate the pacific. I know they use
GPS, but how do they navigate by radio if the GPS where
to fail. Also, who do they talk to once out over the water?
Honolulu center? I know Korean Air and others that head up
to the North Pacific talk to OAK center then Anchorage Center
up in Scott's neck of the woods. Can someone help me out?
Thanks much!
Posts: 955
Joined: Tue May 18, 1999 2:59 am

RE: Pacific Routes

Tue Dec 15, 1998 4:23 pm

GPS isn't the end of inertial navigation. All the planes that fly trans-ocean routes have INS navigation systems. In fact, I don't even think that GPS is used regularly as a primary navigation system in commercial airliners. Inertial nav systems are on most newer airliners of 737-and-up size.

RE: Pacific Routes

Tue Dec 15, 1998 4:24 pm

They do not use GPS as it is not approved by the gov. They use internal flight systems that work out there position a lot like GPS but not quiet and make a short wave radio call every 10 degrees in lat or long the cover If there instruments and computers were to fail they would get out the map and prey alot.

RE: Pacific Routes

Tue Dec 15, 1998 7:34 pm

To enter oceanic airspace, an aircraft needs to have 3 long range nav systems with 2 operating at all times.
Most airlines still use triple inertial nav systems and now some are using GPS. The routes such as the famous
R22 which goes all the way from alaska to tokyo are laid out in lat/lon coordinates. Inertial nav, or INS is a relative system. A crew will program the lat/lon coordinates of the gate position before taxi, then the INS keeps track of all accelerations, turns, climbs etc etc. made by the aircraft in terms of lat/lon. Its a most expensive system yet its theory is simple. If I know where I am when I start, and I keep track of every movement, Ill always know where I am. Kind of like an expensive dead reakoning system. lol
However, with time, INS looses its accuracy and this is called drift. Updating can usually remove most of the drift error. This is why carriers are moving to GPS.
Its super accurate, doesnt suffer from drift and its always exact. What alot of carriers do is to mount dual GPS with 1 INS as backup or dual INS with 1 GPS as backup. You need 3 working long range systems to be legal in oceanic airapsce. As far as comm with ATC. The airlines use what is known as HI Frequency radios.
These have a range of a few thousand miles. If you have ever used a short wave radio you have heard Hi freq. Of course, new technology is coming on line all the time. UAL uses high speed data links to ATC to avoid the spotty performance of Hi freq. When you contact an ATC over the water, this is really a relay station. Your speed, altitude, heading, track, next fix and fix after that are sent by this relay station to the ATC unit and your position is plotted and checked to make sure you have the legal seperation from other aircraft. Once in range of VOR's and land based comm, you switch back to the regular comms and navs.

RE: Pacific Routes

Tue Dec 15, 1998 7:52 pm

GPS has been approved for use ONLY on pacific routes.
Both gentleman are right. INS is still the main navigating system of choice for the airlines. We are always last to get all the goodies. lol
INS has drawbacks though. The newer INS units cant be updated. Updating over a VOR would introduce an error rather than correct for one because the newer units are so very very accurate at the start of the oceanic leg. You can only update over a known fix such as a VOR, NDB, DME fix and these fixes are just not accurate enough to re-program the INS. The older units have drift rates of 1 to 2 miles of drift per hour. The newer units that we now use have as little as a tenth of a mile drift per hour. Like most nav systems, INS was developed by the military. It is still the ONLY nav system that is totally self contained. It needs no signals from outside sources like ground based VOR's or even satelites. You can navigate anywhere in the world without having to depend on any outside signals.
Everything is right in the box. lol

RE: Pacific Routes

Tue Dec 15, 1998 8:18 pm

Also, if GPS/INS fails, if there is nothing else left to do, they will simply fly the headings and times indicated in the flight plan, and will most likely turn up at some place pretty near to where they wanted to get.

aviator_ua: That route going from Alaska to Tokyo is R220, just wanted to point that out...

RE: Pacific Routes

Tue Dec 15, 1998 8:21 pm

Its just an old habbit of leaving off the last zero.
Thanks buddy.

RE: Pacific Routes

Tue Dec 15, 1998 9:14 pm

MD11 is correct. Even though you are navigating with these sophisticated systems, you are also doing it the old fashioned way as a backup. Plotting charts are used to plot position at waypoint passage, 10 mins. after waypoint passage and mid-way between waypoints. This way you can watch your track and it will be very noticeable if you begin to deviate from track. However, this has its drawbacks too. The lat/lon that you are using to plot with is coming from the nav system. If its wrong, so is your plotting. But with 3 systems plus your own plotting the odds of everything going down the tubes is small. Navigation will always be a combination of methods. By using these different methods you reduce the odds of a gross navigational error.
As MD11 mentioned, knowing the winds, you can fly headings that will keep you relitively close to track.
As you can see, no matter how sophisticated the nav systems are there is no substitute for good old fashioned navigation principals.
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Pacific Routes

Wed Dec 16, 1998 4:02 am

Doesn't INS contain Ring Laser Gyros?

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