tigerpic,
I would have lot's more questions about the indications, ranges etc for you.
When you say "oscillation" do you mean a
vibration in the rotor system or a movement of the airframe?
Were you close to vne?
What were these secondary indications;
1. TOT
2. N1
3. NR
4. Acft yawing back and forth?
5. Indicated airspeed change during the event?
6. Audible pressure change?
7. Change in groundspeed?
8. Close to vne?
If the secondaries 1 through 4 were varying I would work the engine/ bleed valve side of it.
5 through 8 would lean me towards unforeseen turbulence/ frontal passage/ lee eddies from something
If those were clean;
And the event was happening at a small power range I would work the engine some more,governor, power demand, load demand etc.
If it's a small airspeed range it's happening at I'd look at the rotor system/ flight controls from the blades back to the servos and then further back the chain to the place you do the touchy feely stuff to.
Keeping in mind that the flight control side of this problem is the most dangerous I would go through all I could on the ground first and with heavy emphasis on the flight controls.
Please let us know what your technicians find out,
(disclaimer....not a eurocopter guy, just tom generic)
