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Has anyone ever had or heard of an engine going to idle during flight in a 500? After a hard landing the engine (C20R) was shipped to RR, tested, and they say nothing is wrong and they sent it back. Just want to know if this has happend to anybody else. The throttle was not accidentally closed. The power just went to idle. The engine is back in the heli but I don't know if I'll get back in it or if anybody should.

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RR250 series are mechanically and pneumatically controlled. A leak in the "P" lines could cause the engine to go to idle!!!! This has been know to happen before.

 

It sounds like "maybe" one of the "P" lines was not reconnected properly or is loose/leaking. N1 spools down to 60-65% or so.

 

Good luck,

 

Mike

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RR250 series are mechanically and pneumatically controlled. A leak in the "P" lines could cause the engine to go to idle!!!! This has been know to happen before.

 

It sounds like "maybe" one of the "P" lines was not reconnected properly or is loose/leaking. N1 spools down to 60-65% or so.

 

Good luck,

 

Mike

 

That’s correct and likely the cause. Loose ”P” lines have similar effects on other engines too. Had a cracked P3 line on a Bell 212 (Pratt & Whitney PT6T Twin-Pac) run the #2 engine to idle.

 

Pneumatic-mechanical fuel controls maybe the most complex mechanical devices install in helicopters. They’re an elaborate arrangement of lines and fittings, small valves, orifices, springs, gears, screens, bypasses, bleed openings, filters, adjustment dials, and pin screws. Any type of contamination in the pneumatic sections of the fuel control or governor will also lead to engine failure.

 

The following is from a fatal accident report related to the 250-C20 and its Compressor delivery pressure (Pc) sensing line.

 

“Before engine disassembly began, it was found that a pipe running between the compressor diffuser scroll and PT governor was slightly loose. This was traced to a loose nut (of a type known as a 'B' nut), at the union of the pipe with the diffuser scroll. The purpose of the pipe is to supply a reference compressor pressure, Pc, to the fuel control components. In the event that the pipe becomes disconnected, there will be a complete loss of engine power; the gas generator will run down to sub-idle and even flame out. The nut could be turned under firm finger pressure, although the engine manufacturer specifies an assembly torque of 80 to 120 Ib/ins for this and similar unions on the engine. It was established that the union was leaking by disconnecting the Pc pipe at the PT governor and blowing air into it; bubbles appeared after soap solution was applied to the union (see Figure 2). Most of the 'B' nuts on the engine had no 'torque paint' applied to provide an indication of loss of torque during inspections, although a white, crumbling residue was visible on a few. Such residue was found on the loose union, and the two halves of the mark were misaligned by approximately 1/16 inch, ie only a small rotational movement. It was later noted that the application of 80 Ib/ins of torque caused realignment of the marks and also eliminated the leak. The Pc pipe is normally disconnected at the compressor scroll whenever a compressor wash is carried out. The aircraft records indicated that this was last accomplished on 2 October 1993, approximately 30 operating hours before the accident.”

 

Fig2PcLine.jpg

Edited by iChris
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Exactly what i was going to say, this very thing happened in the 333, the line had just come unscrewed and popped off on final. The line was on the back side of the engine and a little hard to find, we were all surprised to find it completely unconnected. Engine ran fine, only just above idle.

 

dp

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  • 2 weeks later...

Maybe iChris can help me out with this as it’s been a while since I’ve touched a 500 and I’m older and my memory is,,,,, well older too….

 

I recall throttle rigging being an issue with flame outs and/or spool downs on 500’s. I vaguely remember throttle rigging may only affect the engine when the throttle is rolled off. However, if an improperly rigged throttle is rolled on beyond the “full open” position, could it possibly affect the fuel flow?

 

I know one thing, when flying any helicopter with a throttle grip on the collective; I’m habitually check-twisting the throttle to the full open position.

 

The one thing I’m pretty sure of is; a quick check is to look at the (2) allen set-screws on the throttle in the closed position. They should be pointed straight down. If not, it’s an indication of an improperly rigged throttle.

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I recall throttle rigging being an issue with flame outs and/or spool downs on 500’s. I vaguely remember throttle rigging may only affect the engine when the throttle is rolled off. However, if an improperly rigged throttle is rolled on beyond the “full open” position, could it possibly affect the fuel flow?

 

I know one thing, when flying any helicopter with a throttle grip on the collective; I’m habitually check-twisting the throttle to the full open position.

 

The one thing I’m pretty sure of is; a quick check is to look at the (2) allen set-screws on the throttle in the closed position. They should be pointed straight down. If not, it’s an indication of an improperly rigged throttle.

 

 

That’s true, incorrect throttle rigging can cause engine flameout. The old deceleration check (MD 500 normal procedures section) called for snapping the throttle twist grip from the full open position to idle, then timing the deceleration time through 65% N1. The minimum allowable deceleration time was two seconds. The Rolls-Royce OMM also required that the engine N1 speed not drop below 59%.

 

Not meeting these requirements could lead to engine flameout during a throttle chop or practice autorotation. The corrective action was a rigging check of the fuel control quadrant and pointer. One of the checks was to ensure when the throttle was move from full open to idle that the pointer on the fuel control quadrant returned to the 30-degree mark.

 

The maximum speed stop adjustment (mechanical stop on fuel control) prevents over speeds. The throttle linkage is not allowed to move the throttle shaft lever on the fuel control pass the adjusted speed stop.

Edited by iChris
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  • 4 years later...

Maybe iChris can help me out with this as its been a while since Ive touched a 500 and Im older and my memory is,,,,, well older too.

 

I recall throttle rigging being an issue with flame outs and/or spool downs on 500s. I vaguely remember throttle rigging may only affect the engine when the throttle is rolled off. However, if an improperly rigged throttle is rolled on beyond the full open position, could it possibly affect the fuel flow?

 

I know one thing, when flying any helicopter with a throttle grip on the collective; Im habitually check-twisting the throttle to the full open position.

 

The one thing Im pretty sure of is; a quick check is to look at the (2) allen set-screws on the throttle in the closed position. They should be pointed straight down. If not, its an indication of an improperly rigged throttle.

The screws at 6 o'clock on the pilots throttle (left hand drive) is mid way between cutoff and full open if the throttle is rigged correctly. At cutoff the screws are 5 o'clock maybe 4. Most of the problems with this throttle system seems to with the inboard throttle ring gear being clocked improperly or backlash between the pinnion and ring gear. Also play or loose hardware in the bell crank at the end of the interconnect shaft. If there is any difference between rolling to idle and snapping to idle then you have play somewhere in the throttle system. As for the full open stop be sure per the HMI it contacts the max stop on the fuel control. Anyways my 2 cents I learn something new everytime I rig a throttle on a new to me 500!

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