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power settings vs FF/Torque/TIT


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I’m investigating the cold and low starts on the Allison (Rolls Royce) T56-A-15 engines mounted on the C-130’s.

More than 50% of our fleet suffers from low start and cold starts, if we go further we also see that later on some of the turbines are cracked on their 2nd and 3rt stage. Clearly it is burn thru.

 Low starts are following technical documentation no problem but it’s an indicator that there is something wrong, low start definition for our opinion is the following: between 720° and 780°C TIT with a normal start time.

 Cold start is stated that everything is bad below 720°C TIT.

Normal reaction for maintenance is adjusting the NULL orifice on the td-valve.

In the wiki part you’ll find what we know in the fuel system and temperature management on the engine.


• Our fuel control units are modified to COIL 1536 (commercial overhaul information letter) this means that they reduced the fuel with a ratio of 26PPH during start sequence. (part number 440970-3 or 440970-4) Also there a not many problems with FCU’s and they have an average between 9.000 and 16.000 flight hours without major overhaul. CIT bellows influences the start system, but we cross referenced a few and until now the measurement is in limits.

• Our compressors suffered for many years low zone indication until for a few years ago they did power recuperation, and the gas path is almost optimal, good performances are measured. A regular compressor cleaning is established with hot water and hot soap mixture.

• Thermocouples; these are tested for the electrical junction but cold, also the air inlets are measured for physical deformation. The thermocouples have an H-factor of 75. We bought a new test set where we can measure the out put from the thermocouples when they are heated up, but it did not arrive yet.

• Td-valve, this item has also much flight hours same as FCU between 9.000 and 16.000 flight hours, these parts are regularly send away for repair, never had got an upgrade or parts changed in side. Our td-amplifier is a : branch RAVEN.

• We seldom have problems with the harness and the Y-cable.

• Fuel nozzles, these are tested every 90 day’s. They are removed and placed on a cleaning rig, checked the spray pattern and are put back into system. A new technical compliance is done on almost all of them. The cleaning rig isn’t a calibration rig. Cleaning fluid is used.



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As PJ points out if the start temps are low at "another base" it may just be atmospheric conditions making the temp change.

Also as stated check your "NULL" max power numbers as they will give you an idea of what is happening...

Can you test (or have you tested) your TIT gages?

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these facts and figures are from test bench, other facts and figures are from home station engine runs.

null is the same story, and we have solid states "raven type"

the try with the td amp canon plug removed, didn't do it but will try it!

the TIT gages are electronic, glass cockpit, and test bench fully automatic computer!

thx 4 inputs

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Think of fuel nozzles;

We do have a case that the work done by our repair and testing facility is not according to the standard.

The finding was after getting reports that some of our turbines are suffering from burn through and the cause was found to be "improper fuel nozzles pattern" (based on testing the nozzles attached).

Case approved by sending some of "ready to be useed nozzles" to other agency the result was 70% having a bad spry pattern.

With a bad nozzles some times things become worse when technicians finger TD valve to increases temp a few deg to meet the limits.

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PJ, the canon plug removed.... aint it the same as null operation?

what is the influence in the power settings? ok there is no input of the TD Ampli no more!

very curious!

greetz bob


I've had a few instances where the TD valve was being driven to a PUT or TAKE position, even

with the TD switch in NULL. The solid state amps have been the sinners in these cases.

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