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Is INS Still Used?  
User currently offlineDAL7e7 From United States of America, joined Jun 2004, 357 posts, RR: 3
Posted (4 years 10 months 2 weeks 4 days 1 hour ago) and read 5357 times:

Hey guys,
I just finished a ground school lesson and I was wondering more about the INS. My instructor said that they are big and old and mainly used in airliners but not sure if they're still used. Also, I was wondering if anyone here has much experience with them because they seem interesting and I am curious to know a little more.

Any help is appreciated!

War Eagle!
Trey

(Edited for clarification; class ended)

[Edited 2009-11-03 17:04:52]


DAL7e7 is wondering... Do pilots take crash courses?
35 replies: All unread, showing first 25:
 
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 1, posted (4 years 10 months 2 weeks 4 days ago) and read 5330 times:



Quoting DAL7e7 (Thread starter):
I just finished a ground school lesson and I was wondering more about the INS. My instructor said that they are big and old and mainly used in airliners but not sure if they're still used.

I assume INS=Inertial Navigation System. Yes, they're still used in essentially all airliners.

The old style of INS used physical gyros; big, heavy, expensive, and hard to maintain. Modern INS uses laser gyros; small, light, (relatively) cheap, and reliable. Modern aircraft will calculate position using multiple sources (INS, GPS, DME, VOR, etc.) and then use a filter to combine them to the "best" position estimate (usually GPS is most heavily weighted). INS works great over short term, so it's the best thing to cover temporary gaps in the others, like during a maneuver.

Tom.


User currently offlineL-188 From United States of America, joined Jul 1999, 29799 posts, RR: 58
Reply 2, posted (4 years 10 months 2 weeks 3 days 21 hours ago) and read 5285 times:

God I hope so.

I wouldn't want to be on a GPS only aircraft in the middle of the ocean when the government decides to shut down civilian use of GPS for "National Security" reasons.

Hasn't happened yet, but it is nice to know that a fully self contained navigation system is available.



OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
User currently offlineFlyinTLow From Germany, joined Oct 2004, 521 posts, RR: 0
Reply 3, posted (4 years 10 months 2 weeks 3 days 12 hours ago) and read 5193 times:

It is essentially used on all airliners nowadays. None fly without them. INS is where modern aircraft get their ENTIRE attitude information from, as an INS essentially is 3 gyros and 3 accelerometers, which measure acceleration. They also calculate a position, and the FMS usually mixes this position with other information, like GPS, DME-DME updates, etc., to calculate their own "FMS Position", which is then used for navigation.

In the good old days, the gyros esentially were the gyros you know from cessnas, etc. which actually stabilized a platform in order to keep the accelerometers level. Nowadays, as said before, these gyros are laser gyros.
They basically are triangular-shaped with mirrors in the corners, with two lasers going around this triangle in two different directions. Should there be any movement of the "gyro" around its axis, one light beam takes longer for the now "longer" distance to cover, the other less time. A photocell measures this difference, and a computer behind that does the math to it. The "INS platform" remains attatched to the aircraft without any stabilisation.

Hope that gives you a little more insight.

Thilo



- When dreams take flight, follow them -
User currently offlineDeltaGuy From , joined Dec 1969, posts, RR:
Reply 4, posted (4 years 10 months 2 weeks 3 days 10 hours ago) and read 5157 times:

FlyinTLow, thanks for that good explanation of modern laser gryos. Nowadays you usually only have an 'on/off' switch, and no further knowledge of it after that. Neat to see the inner workings of it.

DeltaGuy


User currently offlineB727LVR From United States of America, joined Jul 2008, 630 posts, RR: 0
Reply 5, posted (4 years 10 months 2 weeks 3 days 9 hours ago) and read 5149 times:

Yeah most lasernav systems on power up will get its present position from the GPS system, but you can still manually input your own cordinates, usually done as an all else fails sort of thing. I like tha lasernav units, they are so much lighter than the old mechanical gyros. Nothing like being in a hurry and send the "help" in to get the new gyro of the shelf, and they come running out carrying it like a briefcase... DOH!  headache 


I'm like a kid in a candy store when it comes to planes!
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4007 posts, RR: 34
Reply 6, posted (4 years 10 months 2 weeks 3 days 9 hours ago) and read 5146 times:

Yes, The Inertial Navigation Unit is the only source on a modern jetliner ( say from B757 onwards) that drives the horizon in front of the pilots. With the latest ISIS (Integrated standby indication system) even that horizon is driven by a laser gyro.(inside the unit)
The position outputs from the INS are integrated with GPS outputs and used for navigation, but where VOR and DME are available, these are usually used in preference.
So if the INS was removed, the laser gyros would still be required.


User currently offlineFlyinTLow From Germany, joined Oct 2004, 521 posts, RR: 0
Reply 7, posted (4 years 10 months 2 weeks 3 days 5 hours ago) and read 5083 times:

No problem, I'd be glad to share some more knowledge on this. We had a pretty smart instructor on this at flight school, unfortunatly I forgot a lot of it by now except for the A320. If there is some more stuff you want to know (including the math behind the calculation of the INS position :P ), just let me know...

Thilo

P.S.: Unless you are a mathematics geek, you really don't want to know  Smile



- When dreams take flight, follow them -
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 8, posted (4 years 10 months 2 weeks 3 days 5 hours ago) and read 5079 times:

From what I recall reading, most airlines use the INS record of the beginning of pushback from the gate as the official departure time of the flight. Does anyone know how true or prevalent this is?


Position and hold
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 9, posted (4 years 10 months 2 weeks 2 days 23 hours ago) and read 5005 times:



Quoting Bri2k1 (Reply 8):
From what I recall reading, most airlines use the INS record of the beginning of pushback from the gate as the official departure time of the flight. Does anyone know how true or prevalent this is?

Several airliners use the INS to get groundspeed, because the air data system doesn't work when you're going slow (or backwards). So it's true in the sense that the official departure time of the flight is the Out time, when the wheels start rolling.

Tom.


User currently offline747classic From Netherlands, joined Aug 2009, 2141 posts, RR: 14
Reply 10, posted (4 years 10 months 2 weeks 2 days 17 hours ago) and read 4956 times:

As a 747 Flight engineer, starting at the mid 70's we had the very extended navigational technical course and had to know everything about the then new inertial navigation systems.

The old (big and heavy ) Inertial Navigation Systems (as installed on the 747,DC10, L1011 and Concorde) worked with gimbals to keep the gyro's in an upright position and used accelerometers to compute the actual position by dead reckoning. (most famous : Delco Carousel IV INS ). The stabilized platform moved free from the aircraftstructure. These systems were extremely accurate and often used in triple installations by civil airliners. From all three platforms the intermix position was used for even more increased accuracy. Position updates were needed, when the ocean crossing started. The only draw back was the relative low MTBF (many tiny moving parts) and the very high maintenance costs for an overhaul. In most remaining aircraft from this generation (70's) the old INS systems are now replaced by laser gyro INS or IRS (inertial reference systems) systems, with GPS update, controlled by FMS, to meet the increased navigational requirements.

The present laser-gyro based systems are strap-down systems (strapped to the aircraft structure) and don't have moving parts. These systems were possible by the increase in computing power in the last 2 decades. However these systems are not so accurate as the old (very expensive) INS systems. So the calculated INS position had to be updated more frequently.
At first auto DME updating was used (eg 747-400 etc). Later multiple GPS receivers are used to update the computed actual position of the INS systems.
On some (updated) aircraft there is even primary GPS navigation, while the INS nav position is updated every 5-10 minutes for standby purposes (total GPS failure).
On all aircraft the INS is still used for attitude info.

[Edited 2009-11-05 01:20:43]

[Edited 2009-11-05 01:31:32]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineFaro From Egypt, joined Aug 2007, 1545 posts, RR: 0
Reply 11, posted (4 years 10 months 2 weeks 2 days 8 hours ago) and read 4863 times:



Quoting 747classic (Reply 10):
However these systems are not so accurate as the old (very expensive) INS systems.

Quite counter-intuitive: why should a 70's-era electromechanical gadget be more accurate than contemporary laser ring installations? I don't understand...

Faro



The chalice not my son
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4007 posts, RR: 34
Reply 12, posted (4 years 10 months 2 weeks 2 days 7 hours ago) and read 4842 times:



Quoting Faro (Reply 11):
Quoting 747classic (Reply 10):
However these systems are not so accurate as the old (very expensive) INS systems.

Quite counter-intuitive: why should a 70's-era electromechanical gadget be more accurate than contemporary laser ring installations? I don't understand...

Faro

Thats what I was thinking.
I wonder if 747classic has any proof.
Looking at the IRS drift at the end of the flight, which I don't do very often, i would say it is much better now than before. But, the reliability is hundreds of times better. On the Tristar, we used to change IRS units every week. They were so unreliable that we fitted a tray with a DG and a VG in the Nbr 3 posn, as there were so many IRS away on repair. In my 25 years at ARN, I have changed 3, two on B734 and 1 on A320.


User currently offlineB747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 13, posted (4 years 10 months 2 weeks 2 days 7 hours ago) and read 4838 times:



Quoting Tdscanuck (Reply 9):
Several airliners use the INS to get groundspeed

Indeed. We use the GS readout from the INS's during taxi on the B747.

Quoting 747classic (Reply 10):
(most famous : Delco Carousel IV INS ). The stabilized platform moved free from the aircraftstructure.

I've heard that is exactly why they named it "Carrousel"

Quoting DAL7e7 (Thread starter):
but not sure if they're still used.

Yes, I still get to fly in an aeroplane with triple Delco CIVA installation.
They are old, extremely bulky and heavy but the perform really well. In a nutshell, all the navigation computer needs is barometric altitude and TAS from the CADC (Although is perfectly capable to operate without them) and present position input for alignment.
Based on what the accelerometers and gyros are sensing, the computer calculates and solves the equations associated with great circle navigation, supplies control information to the inertial platform to keep it earth referenced and monitor itself. In return it provides true HDG; TAS; GS; Wind speed; Wind on nose; Ground track angle; Drift angle; Cross track distance; Present position; Distance; Desired track and supplies guidance to the autopilot/FD system to keep the airplane in a great circle path.

A truly magnificent equipment, completely independant from ground stations/satelites.
It can even operates with battery power in case of emergency.

Regards,

B747FE.



"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
User currently offlineB747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 14, posted (4 years 10 months 2 weeks 2 days 7 hours ago) and read 4836 times:



Quoting TristarSteve (Reply 12):
Thats what I was thinking.
I wonder if 747classic has any proof.

In my experience, LTN 92 are both more accurate and reliable than Carrousels...way better.

Regards,

B747FE.



"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
User currently offline747classic From Netherlands, joined Aug 2009, 2141 posts, RR: 14
Reply 15, posted (4 years 10 months 2 weeks 2 days 5 hours ago) and read 4806 times:



Quoting TristarSteve (Reply 12):
Quoting Faro (Reply 11):
Quoting 747classic (Reply 10):
However these systems are not so accurate as the old (very expensive) INS systems.

Quite counter-intuitive: why should a 70's-era electromechanical gadget be more accurate than contemporary laser ring installations? I don't understand...

Faro

Thats what I was thinking.
I wonder if 747classic has any proof.

Why do people always think that old is bad and new is good.

After more than 25 years experience with the old (Delco Carrousel IV) INS on the 747, I still come to the conclusion that the old system was more accurate or at least equal, when it worked ok. The MTBF was the real problem together with the alignment time during start up of the system.
I have flown the 747 classic with the Delco, Litton 72 and 92 and the tolerance on all three was 3+3T for removal. (T = time in nav mode)
Normally, with 3 normally functioning systems we had an radial error of only a few NM when crossing the Atlantic with the Carrousel IV.


You can get more accurate ring-gyro lasers if you want, but the cost of such a system will be high and it's not necessary to be that accurate, due to the continuous updating capability.
In fact in new aircraft it's for navigation a back-up system.
And,as always, the airlines don't want to pay more than necessary.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineJohnM From United States of America, joined Feb 2001, 347 posts, RR: 0
Reply 16, posted (4 years 10 months 2 weeks 2 days 3 hours ago) and read 4778 times:

Older "legacy" C-5s still have the triple delco INS. I have worked the system for a pretty long time and it is a good system. Easy to troubleshoot, ops check, and repair on the aircraft. Pretty reliable compared to some of the POS systems that plane has. It is being replaced with a laser ring gyro system which I must admit, does work very well and doesn't break much. I always thought the Delco system was so good because it came from the civil aviation world and Uncle Sam didn't modify or screw with it. Somebody else worked the bugs out before the AF got a hold of it!

The only issue in my opinion with old delco stuff is: the frequent (60 day) replacement cycle required for the battery units, and it is difficult and expensive (as mentioned earlier) to fix the box (nav unit) when it goes tits up.


User currently offlineB747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 17, posted (4 years 10 months 2 weeks 2 days 2 hours ago) and read 4758 times:



Quoting 747classic (Reply 15):
Why do people always think that old is bad and new is good.

Not always.
We still use the good old Performance Management System in our planes. Works really good and I am pretty sure we'll never get an FMS on the 747 fleet.

However, the fact remains. While Carousel IV units get the job done, strap down inertial platforms are just better.


Regards,

B747FE.



"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
User currently offlineBigSaabowski From United States of America, joined Jul 2008, 158 posts, RR: 0
Reply 18, posted (4 years 10 months 2 weeks 2 days 1 hour ago) and read 4738 times:



Quoting Bri2k1 (Reply 8):
From what I recall reading, most airlines use the INS record of the beginning of pushback from the gate as the official departure time of the flight. Does anyone know how true or prevalent this is?

None that I'm aware of.
ACARS is used for that. There are several inputs into ACARS, the two most common being the parking brake position and boarding door status. Those two are usually used to determine the out and in times (i.e.: Out = Boarding doors closed with the parking brake released).


User currently offlineRcair1 From United States of America, joined Oct 2009, 1320 posts, RR: 52
Reply 19, posted (4 years 10 months 2 weeks 1 day 11 hours ago) and read 4660 times:
AIRLINERS.NET CREW
CUSTOMER SERVICE & SUPPORT

HP MEMS Could Shake up Motion Sensing

You may find this interesting. A new type of inertial sensor. These are really quite amazing devices...

http://www.pcworld.com/article/18149...could_shake_up_motion_sensing.html



rcair1
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 20, posted (4 years 10 months 2 weeks 1 day 10 hours ago) and read 4648 times:



Quoting BigSaabowski (Reply 18):

Interesting, thanks. I suppose that does make more sense since there's already someone (probably a dispatcher) monitoring ACARS. It would probably require another crewmember action, or some additional communication between the FMS and ground ops, to get the data from the INS.



Position and hold
User currently offlineB727LVR From United States of America, joined Jul 2008, 630 posts, RR: 0
Reply 21, posted (4 years 10 months 2 weeks 12 hours ago) and read 4528 times:



Quoting Bri2k1 (Reply 20):
Interesting, thanks. I suppose that does make more sense since there's already someone (probably a dispatcher) monitoring ACARS. It would probably require another crewmember action, or some additional communication between the FMS and ground ops, to get the data from the INS.

Maybe, but thats what the log book is for. The crews write down their OUT/OFF times. And once airborn (from home station) they call back to the ground and give their times. When they are away, depending on the Capt. they will either call using the sat phone, or wait until the next stop to call back. Atleast mine do. Our aircraft haven't been fitted with ACARS. We haven't quite got caught up to the reast of the world.



I'm like a kid in a candy store when it comes to planes!
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 22, posted (4 years 10 months 1 week 6 days 3 hours ago) and read 4406 times:

Guys, dont mix it up for the bloke. Now I*NS and I*RS have a different letter in them for a reason. NO IRS can possibly be used for NAVIGATION - it is just a referential unit for some other unit (FMC).

Also, typically, IRS relates to laser gyro stuff, and INS to clockwork magic. Though I am not sure it is like that exclusively.



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 23, posted (4 years 10 months 1 week 6 days 1 hour ago) and read 4388 times:



Quoting Fabo (Reply 22):
Also, typically, IRS relates to laser gyro stuff, and INS to clockwork magic. Though I am not sure it is like that exclusively.

It's not. Current generation airliners have IRS and INS, but no mechanical gyros.

Tom.


User currently offlineKELPkid From United States of America, joined Nov 2005, 6381 posts, RR: 3
Reply 24, posted (4 years 10 months 1 week 6 days ago) and read 4377 times:



Quoting B727LVR (Reply 5):
Yeah most lasernav systems on power up will get its present position from the GPS system, but you can still manually input your own cordinates, usually done as an all else fails sort of thing. I like tha lasernav units, they are so much lighter than the old mechanical gyros. Nothing like being in a hurry and send the "help" in to get the new gyro of the shelf, and they come running out carrying it like a briefcase... DOH!

Interesting. I wonder if this is why, in SIN, there is a sign with the LAT/LON coordinates for each gate, at that gate...  Wink



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
25 Mandala499 : There is some truth to it... because the role of the inertial systems has changed. The clue is here: INS = Inertial NAVIGATION System IRS = Inertial
26 MD-90 : So what would happen to international flying if for some reason the GPS system failed and modern 777/A330/A380/etc were forced to get by without GPS
27 Tdscanuck : The airplane would attempt to get some combination of DME & VOR and get a position from that, and it would keep track of it's position via IRS integr
28 Fabo : Also known as The Very Same Way As Before GPS.
29 Mandala499 : Btw, "Crappy IRSes" does not mean they're hopeless... 737 Classics still fly on dual IRS with RadNav position updates... provided they're maintained c
30 747classic : That's the exactly the point I made before : Mandala 499, I couldn't have explaned it better. The incidents you mentioned are all caused by a lack of
31 Bri2k1 : I hate to get off topic, and I don't know the specifics here, but I would be interested to find out more. DME provides slant range, not absolute posi
32 Post contains links and images Mandala499 : The thing is, do you need to be more accurate than 0.1NM in cruise? The GPS Pos received by the FMC is displayed on the ND in this case (777) by the
33 Bri2k1 : Interesting, Mandala499, thanks. I am not yet rated on the 777 either ( ), but do you know why there would be more than one GPS location symbol? GPS p
34 Tdscanuck : Because you've got more than 1 GPS. I think the 777 has 3. You have 3 GPS receivers. One is dying. By looking at the display, you can probably tell w
35 Mandala499 : Bri2k1, The 777 has 2 GPS receivers (GPS A, GPS B, or is it GPS L and GPS R... can't be bothered to open the book), and 3 IRS, with the multiple radna
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