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Litton INS - LTN-72RH

Old 23rd Apr 2020, 14:28
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Litton INS - LTN-72RH

Hi there - there is a long history of various inertial navigation systems from Litton from very early
mechanical ones until recent ones based on [email protected] gyros and GPS fusion. Recently I obtained a
LTN-72RH made by Litton Aeroproducts, Canada; part number 1520°0-05-02-36-71, serial 2836:

This unit obviously is of the latest generation using mechanical gyros on a gimbaled platform...

...together with a digital computer for navigation and user interaction. I have essentially three
questions on this unit and I am sure lot of experts and/or users should be in this forum:

(1) Does anyone know, where this LTN-72RH was used - I have been told, it was on DC10-300,
but not sure on this. Also would be interesting, what the additional letters "RH" mean - probably
some radio-nav addon included (Software revision is 72-71-06)?

(2) Of course: Any manual/schematics/pin-outs around helping me to better understand or even
fire up this unit? BTW: I have some experience in making equipment like this work again ;-) -
see my work on a
or an

(3) Which CDU does match the unit? From the WEB I know a very old type of CDU as used with
LTN-51 (Concorde and probably many others)...

Than there is a midle aged CDU which obviously already has alphanumeric displays:

And I came accross rather modern CDUs by Litton which more look like a FMS:

Any hints/discussion/comments are welcome...

Best wishes, Erik - erik - at -

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Old 24th Apr 2020, 09:34
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I dont know if these people can help
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Old 24th Apr 2020, 11:03
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I associate the first CDU as being used with Litton INS, I have never seen the two later CDUs. I worked with multiple operators over the years until I retired in 2008. And would expect to find that equipment on DC10-10 and -30, Tristar and 747 2/300.
Concorde which you mention was as far as I am aware Carousel equipped.
Carousel was a quite common fit to Tristar too. Litton more usual on DC10 and 747 but as ever the fit was an operator option.
I do remember the INU being heavy !
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Old 24th Apr 2020, 11:40
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Hi, thanks for the answers! Will try my best with the guys at the VMARS, although they may be centered on radio stuff? Thanks also to Wodrick, yes, the unit is very heavy (25+kg), so for the tree units probably having been on the DC10 this makes the weight of an additional
passenger ;-)
I have seen in document 34-42 on the DC10, that there should have been three INUs and one CDU. But the first CDU in the series (which I actually have got) does not have the propsed switch to select which INU's values to show on the display. Also checking some signals on this CDU they do not match what is given in the sheet 34-43-1 I have got on the DC10, so there must be a different kind of CDU still...
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Old 24th Apr 2020, 13:11
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As the aircraft age then they get modified. "My" DC10s both 10-10 and 10-30 had triple installations with three CDUs one for each pilot and a third in the roof panel, usually over the Captain's head. I worked on DC10s from four different companies and all were different in some respect.
Have fun, sorry I can't help further, as I retired all my manuals and notes went to the recycling.
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Old 24th Apr 2020, 18:31
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Thanks for your comments, Wodrick! Sad, that your notes etc. went to the recycling, but can understand this after your retirement. Probably you remember whether you often encountered failures in these systems? I guess the navigation computer calculated a mean/most probable position from the input of the three drifting INS systems? Perhaps it is to long ago to remember how much miles they have been off position after e.g. crossing the atlantic?
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Old 24th Apr 2020, 22:23
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Originally Posted by baigar View Post
Probably you remember whether you often encountered failures in these systems? Not often, pretty reliable
I guess the navigation computer calculated a mean/most probable position from the input of the three drifting INS systems? You get ahead of the technology ! Each INS fed the on-side flight director/ Autopilot with a simple switch NAV/INS. either side could be selected to the alternate.
Perhaps it is to long ago to remember how much miles they have been off position after e.g. crossing the atlantic?
I might be confusing other systems, trans Atlantic up to eight miles or so. Could often be less. When they got to a consistent 20 miles or so time to change INU. In my company it was a Tech Log note INS Drift #1,#2,#3.
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Old 25th Apr 2020, 10:38
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Wow - cool; thanks for the information. So good to know and for the long flight time over the
Atlantic, 8 miles are not so bad. The military Ferranti systems from the 1970ties I restored
and have one working one mile per hour is claimed, although I guess they rarely really
where that good. You also have been pretty right, that there are lot of very different configurations
of panels if one looks at cockpit pictures on the WEB! In a PanAm manual available online I found
the following panels related to the INU kit (Claimed to be a DC10-30):

A mode selector panel:

Than a sensor display panel (with switch to select one out of three sensor units):

And what they call CDU, an unit doing navigation already with waypoints etc.:

So the search for the right panels will go on and I will check, whether the sensor pinout matches
what I have got...
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Old 25th Apr 2020, 18:26
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The pt. No. of your INU is: 452080-05.

The TSO for that unit is TSO-C5C which shows a LTN72 control panel as pt. No. 452090-02

That would suggest the first control panel depicted above, with the Dim selector in the middle, would be suitable. Litton were taken over by Northrop Grumman.

Inertial systems at the time had allowable drift of X number of miles.

Where X = 3+3T and T was the sector time.

For example, an 8-hour flight would mean the maximum allowable drift would be:

3 + (3 x 8) = 27 miles. The systems were quite reliable unless not used for some time, in which case they tended to fail at start up.

I have no idea what the RH represents, There are R and RL models as well.
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Old 26th Apr 2020, 10:25
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Hi QA1 - many thanks for your informative post! Given the part number for the LTN72 panel, I
indeed found a pictures on AeroBay - the panel indeed looks quite similar to the first, oldest
ones on my first posting. The panel I have got looks identical although it has got a different
part number.
There is a catalog of commercial items available from Northrop Grumman giving more part numbers
of various navigation kits - so also thanks for this hint! Will be a good starting point for more
Thanks also for the formula on calculation of accuracy. Of course this linear+offset one is
some estimation - from a physical point of view (and what I saw in my restored systems) is,
that there usually is a strong oscillatory component in position (Schuler period) too ;-)
Thanks again for all the input!!
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Old 23rd Sep 2020, 08:38
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I do know a bit about the construction of this Litton P-1000 4 gimbal platform. It has two G-1200 non fluid floated tuned rotor ball bearing gyroscopes each capable of measuring two axis of rotation. The rotor uses a heavy tungsten wheel with precision machined mechanical flexures similar to the Kearfott "Gyroflex" dry rotor gyro. The three A-1000 accelerometers are non fluid floated hinge restrained force rebalanced. They use speaker type coils and permanent magnets for servo restraint. Both inertial instruments use Invar as their main structural material for high thermal stability.

Similar Litton P-1000 platforms have been used on the early U.S. Air Force F-15 fighter aircraft, the A-10 Warthog attack aircraft, some of the early versions of the U.S. Air Force air launched AGM-86 ALCM and U.S. Navy AGM/BGM/RGM-109 Tomahawk cruise missiles.
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Old 23rd Sep 2020, 14:45
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Hi there - thanks for the input! Sounds quite interesting - if you have more stuff to share, you are welcome to get in touch via email at [email protected]! Yeah, the unit look very interesting and meanwhile I got some documentation from a Laker airways DC-10 showing the pinout of the unit and which is according to my first measurements accurate. I also obtained a matching CDU panel recovered from an Atlas 747 being scrapped in Rio/Brasil and a mode selector panel from eBay. So I have all stuff to give the unit a try but need to prepare some experimental cabling and then it is going to get interesting ;-)
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Old 25th Sep 2020, 20:00
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I think the litton 72 was a follow on from the 52 which was a fixed platform, lots of the older 707s had 52 and were limited to latitudes because the ins couldn’t cope beyond certain limits, the 72 was much better but still not as good as the carousel
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Old 26th Sep 2020, 13:19
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Hi Rimmer, thanks for your posting - yes, the 72 is derived from the 52 but this also had a gimbaled (not fixed) platform. Those days all these systems worked like this for some reasons (1) the instruments are much more accurate if they are not rotated throughout the flight as e.g. each accelerometer also measures a little of the rotation. (2) Computation was much more easy if the accelerometers measured N/S, E/W and Up/Down - so one stage of transformation was omitted in this way. (3) Just by routing the signals from the platform sensors via buffers to the plug of the unit, attitude signals are available which are very accurate and for free - these where used in the attitude indicators etc.
The later carousel units slowly (minutes) and constantly rotated the platform with the instruments thus averaging out any bias in the N/S and E/W accelerometers - that was a really clever idea... Have a good time, Erik.
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Old 21st Nov 2020, 00:39
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So, i managed to get my hands on a LTN-51 CDU (PT NO 663550-04-01) and I noticed it on one of your photos and im trying to power on mine, do you have by any chance the pinout for it? At the time i have only figured out that pins b and a (E and D on the J2 connector) are used to turn on the lights for the numbers, DIM and WPT.

I was also wondering if anyone had any idea on where did this bad boy flew. Its serial number is 0983 and its manufacturing date is 9-20-74.

Any info helps at this point, so thanks in advance
BTW: Awesome job with the FIN-RPMD!!
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Old 23rd Nov 2020, 17:50
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Hi there and thanks for the positive words on my FIN1010 and FIN1012 related work! It is still an exciting journey and almost daily interesting learning! Cool to see, that others out there also have some interest in these systems!
My focus in this thread is the LTN-72RH I obtained to see the difference to the UK made Ferrantis, so I do not have got any information spcific for your LTN-51 CDU and maybe this pinout (acquired with the help from the nice guys here - THX!) does not match your CDU (although it also has got two plugs, your known pins do not the pinout I have got). So probably not of much help for you:

Just out of curiosity: Do you have got a LTN-51 and what are your plans? Do you want to fire it up or are you just interested in lighting up the CDU for some purpose?
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Old 23rd Nov 2020, 20:17
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First of all: THANKS FOR THE HELP!, I'll try to make some sense of it when I get home and I promise to let you know if I manage to get something to work.
I don't really have any plans for it since I only own the CDU but at the end I would love to be able to fire it up!
I found the CDU inside a Learjet (Probably a Learjet 25) that someone cutted in half at a local airport (MMJC) for a project that never came through. The CDU is missing some of the minitron displays (I've only got 5 of them) and both of the knobs but its pretty much complete (BTW, if anyone's got some extra minitron displays I'll be happy to store them for you haha).
Also, there is a LTN-51 INU that supposedly belonged to a Concorde for sale on Ebay if anyone's interested (I would post the URL but i'm not allowed to do it until I have 10 posts, sorry)

If anyone else have any other info or advice for me I'll be very gratefull

PS: If you want, I can try to post a photo of the CDU later
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Old 30th Nov 2020, 02:44
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So, I've been trying to figure out the pinout and from what I understand it states that I should plug the 28VDC into the a and b pins on the J2 connector but those connectors are bridged over each other (they share the same cable). However, it looks that those pins on the J1 may be the one's I'm looking for (although the pinout says that those are not used). Am I reading the pinout correctly?. I also noticed that, in the pinout all the lower case letters have a "_" below them and in my connector, only a few of them have the "_". Is that important for some reason?.
The other pins I found (E and D of the J2) are correctly stated in the pinout so, just for the fun of it, I reassambled the CDU to see how the lights looked like and I have to admit that they do look pretty cool haha (I would post a photo but the site doesn't let me do that yet).

I'll keep you posted when I find any other clues and as always I would appreciate any other info anyone might have!
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Old 30th Nov 2020, 08:00
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Hmm, as I stated - the schematic above matches my LTN-72 CDU and I also have CDU (3) from the first posting where the pinout does NOT match. Probably the CDU (3) above is what you have got, too. But I guess the basic functions are the same as are the internal electronics. As you discovered: Probably only some pins are swapped. Would be cool to see a picture of your illuminated CDU ;-)
Unfortunately I had no time so far, giving my CDU+LTN a try although the test cabling is prepared. Here for reference the two control panels I obtained/resuced over the last weeks to go with my LTN72-RH:

(A) A Mode-Selector panel, type 452100-02-03, serial 6825 from a scrapped Atlas airliner:

(B) A CDU, imported from Rio/Brazil (AeroBay made a good hobbyists price); type 452090-02, serial 0265 and it came even with paperwork and test protocol dated December 2010 and the origin was a scrapped TAP aircraft:

Will post an update after first tests - but probably not before February 2021 due to the pandemic...

Last edited by baigar; 1st Dec 2020 at 08:28.
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Old 23rd Mar 2021, 23:02
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Ex DC10 driver here...I can shed some light on this.

These units were indeed DC10 fit

The first unit is the Litton 72. From memory only 9 waypoints could be entered in sequence, all using Lat and Long co-ordinates.

The second unit is the Litton 92 which had a database containing user waypoints which saved entering Lat and Long co-ordinates.

I think the 92 had 100 waypoints that could be strung together simultaneously to create your route.

I have both these units on my shelf and used both during my years flying the DC10 itself.

Waypoints were entered on one unit only whilst the other two were set to ‘slave’ or RMT. The waypoints would then automatically be transferred into the two ‘slave’ units and after completion of data entry all three units were placed into AUTO and made their own calculations as to their position. This would in turn provide the triple mix position to the Navigation system and reduce position error. Radio updates from DME/DME would periodically bring about a course correction. When flying trans Atlantic and passing Lajes, the aircraft would get a radio update and would usually turn slightly to put itself back into the exact position.

Accuracy of the units was pretty good. Usually less than about 0.3nm/hour of operation from what I can remember.

Like all INS systems, POS INIT at the start of the flight was quite critical as getting it wrong on the ground meant the boxes couldn’t be re-initiated once in flight.

I still have the user manuals for both these units from the manufacturer and the Lam Schematics for the aircraft fit.
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