B212 failed rotor engagement

[before landing check list]

Lets talk about rotor non-engagement during start on the B212. As I understand it, the 1st engine started should have the Np about 80-85% which is a good engagement speed (critical?) and when the second engine is started it's Np can go past the Nr. The big problem is compounded when the second engine re-engages the system. Am I in the correct ball park here? If I can be supplied with references I would be much obliged since I will be teaching this very soon.

Thanks guys

[before landing check list]

Lets talk about rotor non-engagement during start on the B212. As I understand it, the 1st engine started should have the Np about 80-85% which is a good engagement speed (critical?) and when the second engine is started it's Np can go past the Nr. The big problem is compounded when the second engine re-engages the system. Am I in the correct ball park here? If I can be supplied with references I would be much obliged since I will be teaching this very soon.

Thanks guys

[Shawn Coyle]

Not sure about the civil 212, but the military version, 1st engine start only went to idle, and then to 71% N1 for generator load when starting second engine.
Never heard of second engine not engaging directly to rotor at appropriate N2 speed.

[Winnie]

Our checklist have us start 1 (or 2), 71% Ng for gen, then 85% NR for starting #2 (80% if cold outside, which happens frequently where I fly). then start second engine.

Hard engagement I believe is what you are asking about, and would be possibly damaging to Cbox. This would be when the acceleration of the second engine causes the freewheel to grab, possibly damaging internal components.

A non engagement would mean broken Cbox.... Don't think it is possible even to get NP higher than NR.

Cheers
W.

[gulliBell]

I have never heard of non-engaement of the rotor on B212. If you are talking about hard engagement in the cbox when the 2nd engine is started (that is, when the output speed of the 2nd engine exceeds that of the 1st engine with very little Tq on that engine). Can I suggest you refer to the B212 RFM because it is mentioned in there, as well as what to do should you encouter it. By teaching what is written in the RFM you can't go wrong!

[Brian Abraham]

As Shawn has said, never heard of non engagement on start. Nevertheless, I would say it's not an impossibility. Had an occasion of winding the throttle to idle on a Huey for the cool down and was disturbed from my reverie by the sudden realisation that I could count the blades as they swept around. The clutch had not re-engaged, and a hasty shutdown was performed, with the thought in mind of what damage a sudden re-engagement might cause. If a non engagement can happen under those circumstances, I believe the possibility is there for a non engagement on start as well.

[gulliBell]

?...As I understand it, the 1st engine started should have the Np about 80-85% which is a good engagement speed (critical?) and when the second engine is started it's Np can go past the Nr....

The output speed of the power section is known as N2. After the 1st power section is started its N2 is set to 85% which is the optimal rotational speed inside the combining gearbox for the engagement of the the 2nd power section after it was been started. If there is a mechanical fault in the combining gearbox it is possible for the 2nd engine N2 not to engage properly, in which case it will accelerate past the N2 of the first engine, but without driving the NR with it. So with that engine not engaged it will have zero or very low TQ indicated but with N2 higher than 85%. Most likely there will be unusal noise apparent as well.

The corrective action for this fault is mentioned in the RFM. You don't get a 2nd crack at starting the engine as the cbox needs to be removed for maintenance prior to further operation.

This is a very rare event. I have started PT6 twin-pacs thousands of times and never seen an instance of hard-engagement. And Brian Abraham has started them many times more than me, and he says he's never seen it either. However, as I said before, for the purposes of the OP just teach what is mentioned in the RFM.

[before landing check list]

I have never heard of non-engaement of the rotor on B212. If you are talking about hard engagement in the cbox when the 2nd engine is started (that is, when the output speed of the 2nd engine exceeds that of the 1st engine with very little Tq on that engine). Can I suggest you refer to the B212 RFM because it is mentioned in there, as well as what to do should you encouter it. By teaching what is written in the RFM you can't go wrong!

That is my point exactly. Assuming that the 1st engine Np(N2) is married up with the rotor which is a safe bet (Nf/Nr) (that is, when the output speed of the 2nd engine exceeds that of the 1st engine with very little Tq on that engine) then you have a non-engagement eh? A reverse needle split with RPM. I went to Flight Safety/Bell for my 212 initial and I seem to remember hearing about this remote possibility and it is normally cause by the sprag clutch NOT engaging as opposed to Had an occasion of winding the throttle to idle on a Huey for the cool down and was disturbed from my reverie by the sudden realization that I could count the blades as they swept around non-disengagement. Is this correct? I think it is however I would like other opinions.

Thanks all

[gulliBell]

Yep....during start with one power section operating the N2 is matched to the rotor speed, unless of course the rotor brake is engaged in which case I'd be more concerned about that rather than a hard engagement of the 2nd power section!

I vaguely recall an instance long past when a pilot started the engine and didn't get any engagement of the main rotor...attributed to maintenance having been done on the MDS and the replacement MDS hadn't been fitted :}

[Brian Abraham]

non-disengagement. Is this correct?No. The N2/Nr needles split when the throttle was wound to idle, but the clutch failed to re engage when the Nr fell down to match the N2. The Nr was merrily on its way to zero RPM while the engine (N2) was happily running at idle.

[before landing check list]

Found this in the RFM...thanks guys

CAUTION

ENSURE SECOND ENGINE ENGAGES AS THROTTLE IS INCREASED. A NON-ENGAGED ENGINE IS INDICATED BY 10 TO 15% HIGHER ENG RPM (N2) THAN ENGAGED ENGINE AND NEAR ZERO TORQUE. IF A NON ENGAGEMENT OCCURS, CLOSE THROTTLE OF NON-ENGAGED ENGINE, WHEN NON-ENGAGED
ENGINE HAS STOPPED, SHUT DOWN ENGAGED ENGINE. IF SUDDEN (HARD) ENGAGEMENT OCCURS, SHUTDOWN BOTH ENGINES.

MAINTENANCE ACTION IS REQUIRED

So, this can happen. You will see the second engine RPM more than the engaged (also Nr).

[gulliBell]

... Or you might go through a whole career, like several of us here no doubt, and not see or hear of this malfunction at all. Apart from letting students know of the possibility, I wouldn't get too involved or devote much time to the topic during the type technical phase of the B212 initial course.

[pilot and apprentice]

During sim sessions I've seen that the instructions (that I have dealt with) generally present this failure (SPRAG CLUTCH FAILS TO ENGAGE ON START) once per crew per session. If it is mentioned in the groundschool, and C-box functtion is covered, then it should be an easy exercise to diagnose.

All operators for which I have flown the 212 have expected a call (2 crew) or mental note (single pilot) during the start sequence that the sprag clutches are working appropriately during start/shutdown.

But like others, I've never seen one fail myself, or on an operation I was with.

[oleary]

This is a very rare (non-existant?) event now, but it did happen in the early days of the 212.

As someone mentioned, the RFM is very clear on identification and correct action.

... and yes, I always gave it as a sim exercise just so the guys knew what it looked like.