Max Contingency checks?

[ronnie barker]

Hi there, i am trying to find out why max contingency checks are carried out, what would cause them too fail and also what would cause a sloppy feel in the cyclic stick when carrying this out with an associated airframe vibration.

many thanks for your assistance.

[ShyTorque]

The main gearbox is about to come off.

[HeliComparator]

Maybe you should give us a clue as to which type you are talking about?

Max Con checks can fail for a wide variety of reasons, eg incorrect FCU limit stop, TOT limit reached before specified power reached (dirty or damaged engine), fuel flow restriction (eg carbon deposits inside delivery pipes in hot part of engine due to inadequate purging on shutdown). It is however hard to think of an engine/transmission malfunction that would cause the other effects you mention - apart from ShyTorque's hypothesis of course:uhoh:

HC

[ronnie barker]

i am specifically talking about the Lynx GEM engine max contingency checks

[MightyGem]

Why don't you go down the hangar and ask a Reem? Or phone up ATIL at Wallop and speak to Mick Zedzee(Sp???).

[nodrama]

Have a read of the procedure for carrying out a max contingency check on the Lynx, and look at the parameters that it asks to be set and to be recorded…and then think about why.

Basically, the check is to ensure that an engine can provide enough power, without exceeding set limits, to keep the rotor speed within a % margin to keep the helicopter in the air. A/c weight, collective pitch setting (Tq), OAT, aircraft speed and density altitude are all factors to consider.

Think.... 'a twin-engined helicopter is taking off, with little forward speed, and an engine fails. What does the good engine have to achieve?'
That's why we do max cont checks.

Think about why an engine wouldn't be running as efficiently as it should, and that should give you a few clues as to why an engine might fail its check.

Sloppy cyclic? If a helicopter starts to loose height, what does the pilot do with the collective? What affect does this have on the pitch of the rotor blades? What happens next if blades can’t produce any more lift ?

[dipperm0]

Hi

Not sure I have the right answer but, when carrying a max contengency check on a GEM engine, the pilot must pull up the collective to try to reach a defined Ng value, thus, usually, the Nr drops below 100% ( down to but not below 96% if I remember). During that check, the cyclic is sometimes "sloopy" due to the low RPM of the rotor...

DO

[Two's in]

An easier route to establish the reason for Max Con checks on the Lynx is to look at the course of action if the engine fails the check - carry out a compressor wash.

On the Lynx you are confirming that max power measured as engine torque (with the engine not under test back at Ground Idle) is attainable within the parameters for Nh and T6, against measured air density (altitude) and outside air temperature. When it fails, it is usually a function of a "dirty" ECU.

Max Con checks are routinely carried out as a scheduled maintenance op, if engine power is suspect and following an ECU change.

The vibration and handling are simply because you are pulling max power and batting along at a fair rate of knots. Even on one engine, the Lynx is still pretty powerful at a couple of thousand feet. No reason for the cyclic to feel unusual other than you are likely to have it well forward associated with an arm full of collective. The Nr gets lower than usual, but it shouldn't be too low

Red Hot tip -When you are about to test the other engine always, always, put the original ECL back to Flight Idle before retarding the second one to Ground Idle, unless you wish to experience some new CWP captions.

And Mighty Gem is correct - Mick Dzedze knows more about this stuff than most people have forgotten, just give yourself lots of time to hear the answer.

[[email protected]]

The Max con check is usually completed post ECU change to ensure that the Ng governor is set correctly and the expected values of Ng/T6 can be reached without NR decay - ie that the engine is performing as advertised and therefore the performance figures from the ODM are reliable (predicted height loss/Min SELF).

If the Nr decays before the figures are reached, the Ng governor is set too low (had this on a couple of occasions).

If you get a sloppy cyclic in a Lynx, I refer you to Shy Torque's diagnosis or you have inadvertantly switched off the stick trim:)

If the engine fails the max con check then industrial comp wash is next followed by further max con then governor adjustment - after that it is time to phone Rolls and talk replacements.

[Max Contingency]

I carry out the Max Contingency checks to make sure I dont forget any of the essentials. I tend to use, "passport, credit card, toothbrush and condom".

Max

[MightyGem]

Dzedze
Yeah, I knew my spelling was wrong. :O

[[email protected]]

Max - what is wrong with 'spectacles, testicles, wallet and watch'?:)

Mighty Gem - I thought there was a 'j' in Mick's surname somewhere but I can't remember where. Still an awesome scrabble score on a triple letter bonus!

[nodrama]

You've told us before that you are studying for a Foundation Degree, so I assume the original question is part of your course.
The posts so far all indicate that a sloppy cyclic and airframe vibration isn't experienced during a max cont check on a Lynx.
That's the whole point of the question....it's theoretical...to get you to think about what would have to happen, and why, during a max cont check that would cause these things to happen.

[MightyGem]

Mighty Gem - I thought there was a 'j' in Mick's surname somewhere but I can't remember where.
There could well be, but you saw my attempt. :O

[jonwilly]

Max contingency checks.
Ask a Reem says Mighty Gem.
Well when young Will joined his first Lynx equipped unit, I can honestly say I have never hears so much Sh1t talked about a subject as this one.
I was listening to guys who had been on Lynx for years telling each other what they thought they where on about and arguing quite seriously.
I was baffled.
Then I notice out Navy Chief shaking his head.
What are they on about says I ?
Hello we've not met have we?
No but
John think what you called on Scout a Topping Check.
Suddenly all was clear.
Topping Check to ensure the Gas Generator Section of the Engine (N1) will always delivers enough 'Gas' to "Spin"' the Power Turbine to it's max 100 or 100 + % as laid down in manufacturers manual.
john:)

[nodrama]

Question answered Ronnie?

[Misformonkey]

Thought the PPI was a thorough check of both NG (compressor) and PTIT (Hot End) , that is why it is carried out at timed intervals as opposed to post maintenace or post fault. Max Con is basically fuel flow and fuel burn hence why fuel ftg stops come into play, The Max con NG and Ptit are a lot higher than PPi figures.

[Redbeard]

:ugh:

well after having flown about 6000 hours on a lynx..with GEM.. there is no connection between a max. contingency check and sloppy cyclic and aircraft vibraton. :=

Max. cont checks..never fail.. you just reach a max value.. either TQ, or NH or T6.. aircraft vibration... depends on your speed and good vibration analysis. 96 % Nr with max cont. better that you check something else...

sloppy control on a lynx at 10.000 feet ... not at sea level even with max. cont. :ok:

[ShyTorque]

C'mon chaps, seriously!

Surely we are just talking about another expression for a power assurance check?

The engine is run up to max contingency to prove it can actually comply with the manufacturer's declared power output without being limited by EGT or incorrectly governed at too high an N1.

[nodrama]

What was it that Jonwilly said?.....


I have never hears so much Sh1t talked about a subject as this one
:)

Max contingency check is a power assurance check. It's to assure the engine can be worked at max power, keeping Nr in limits, without being limited by temperature or N1.

PPI provides a trend to monitor the condition of the engine, and bring to the attention of the operator any deterioration in it's performance. That's why you've got that page in the M700 to plot and record the figures on a graph.

[Redbeard]

:sad:

read

not about PPI

guys... NO LYNX .. just don't put message.. you don't know the aircraft:ok:

[hoistop]

Maybe I can help a little as maint engineer - eventhough not on Lynx but 212/412, EC 135, A-109.. (and some big jets too)
On PT6T engined 212/412, topping check means spinning one engine to the Ng RPM limit - actually running it to the limit. The purpose is to check if engine RPM limiter and condition of engine actually allows the engine to achieve max. Ng RPM. If not - adjustment of FCU or/and comp. wash is required. In some conditions (dense air) it is difficult to achieve, as Torque limit might come first. Since this is streching the engine to the RPM limit, it is normally done only twice a year - under current PWC maint. schedule. Normally, it is done on the groud with ballasted helicopter to prevent take off. It can be checked also by putting a "wedge" under mechanical stop on FCU and checking this limit with reduced RPM. (called part power check)
Power assurance check is merely an indication if engine is delivering minimum advertised power, thus validating helicopter performance charts. Following FM, it should be done daily (I wonder how many of you are really doing it).
The point is, as you know, to set a certain torque output and, depending on athmospheric conditions, this torque shall be achieved with certain Ng and ITT values. Graph provides you with max. Ng and Max ITT for conditions given. The difference between actual ITT and graph ITT is called ITT margin (and same for Ng margin) and tells you how much wear (and where in the engine - is it compressor or turbine) you have and which limit you might hit first in high altitude/hot OAT. As engine gets older, ITT and Ng margins are of course gettting lower. Typically, after compressor wash, Ng margin will improve. These numbers are also tracked as "engine trend monitoring" and can sometimes give a clue on engine trouble.
Honestly, after 20 years in maintenence I can say that readouts from "steam gauges" are so notoriously unreliable, that trend monitoring them is more guesswork than actual monitoring. Things are much better with FADEC engines and more accurate instruments and readings. The only real check I would bet on with "classic" engines is to perform single engine climb - taking your charts for single engine climb and actually doing it on single engine with max cont. power on a calm day with exact weight - initially it will be torque limited, but with altitude, it will switch to Ng or maybe ITT limit. With stopwatch and accurate climb profile, you determine your rate of climb at certain altitudes (so you can accurately enter in your single engine climb graph)and that gives you a good idea on your helicopter performance - the trick is, that engine power itself might not be everything -it is also flight controls/rotor RPM setting, blade condition etc. that determines your performance.
My five cents worth.

hoistop

[jonwilly]

Excellent post Hoistop.
It's 20 years since I was last involved/doing Lynx PPI and Max con checks.
Engine performance checks to keep matters simple.
Memory says that in the early days of Lynx, the first Twin for Teeny Weeny Airways, many Engineers got off on the wrong foot.
Some folk myself included where never happy about 'Destroying Power' from a good engine, Basic Engineering training.
The two engines had to be balance to within a 'Couple of %' of each other and it took time and experience to be easy about reducing the power of the higher engine and bringing it down to the output of the "Worst' engine.
Still it became all straight forward when basic matters had been explained and PPI where Normally done on a return flt to base by Experienced aircrew saving a Formal Air test.
john
Nice to see this Old Bug Bear is still confusing the yooff of taday.