SA-341 Gazelle accident suggestion

Hi to all!
Name is Darko and I am working in Serbia & Montenegro AirForce as a
flight instructor on SA 341 Gazelle helicopter. Recently I was involved
in an incident, luckily both student and I are ok, dough my beck hurts
a bit. Now, I am working as an instructor for some three years an have
loged so far about 350 houres in total for past five years I'am
working. Newertheless, I am banging my head ever since that day, 5 days
ago, trying to dig out what has happened. So I was thinking, maybe some
of you folks can think of something that I've been mising. Curently
I'm waiting to see what will be the findings of the investigation,
and, here is the story:
SA-341 Gazelle, about 20-25 years old. One day befor incident, she was
gone to the nearby mountain of about 1800 meters to drop and pick up
some relay workers. Everything fine. On the day in question, I started
her up first, where the mechanick worned me not to give her 20 sec of
buster fuel pump but shorter, becose turbine temperature (T4) is
jumping very fast. So I gave her about 10 sec, and the indicator stand
sstil, but then rushed thro and went all the way to almost 700, aldough
I released the ignition switch when she was passing 250-300. I switched
the fuel pump off, te engine rpm's stabilized on 25500 (idle), I
switched pump on again. I flu some trafic patterns for about 20 min,
then other gyes took her for some 40 minuts, then again me with student
on 30 minuts hovering exercise, and then another student came for his
30 minuts hover exsercise, but got only 5 minuts. After that chopper
was totally destroyed and we were 10 meters away standing in disbelief.
Time 10:35 AM. OAT 7C. Calm, no wind. Helicopter in the air for about
1h40min, spent some 250 liters. Student was hovering at 3.5-4 meters
for abote 2-3 minuts and it was going fine, though was strugling to
keep her over spot, but no big deal, he has about 40 minuts of hovering
in total before. Then, the chopper has her nose up for some 10 degrese,
I took over sayng, whell, no need for that, I lowered the nose to
normal atitude, using only cyclic, no need for enything else, then,
about one secund aftr my corection, she started to fall dovn, like
somebodi lovered the colective all the way down. No notisable nose
up/dovn position, no banks, no yaw, just more/less straight down. It
was intense, so I pulled the colective very harsh, while we were
about1.5-2 meters, already thinking, man, I reali pulled it, we're
going to get to 5-6 meters atleast when she settles. Grass. Big
grass. Bang! We hit the ground like there was no rotor above, the left
skid has colapsed, the rear end, she hit with her tail, broke the
fenestron, blades strucked the tail turbine chaft, no tail rotor now,
we're going to the left hard, strong intense forces, I'm lovering
colective all the way down, she is braking in pparts, she done 2 and ¼
turn with nose high, nose low, hiting and dying in agony. that's it,
good by. Whell, after 3-4 sec, I looked, saw I'm alive, the student
too, engine runing on idle! Tried to shot her down, no way, puled the
fuel cut of valve, all the switches, nothing, though the engine rpm
lever was left stuck in front(43500) position. Hit her hard, she came
in back, but engine is stil alive. Whell, after, 2-3 minuts, a mecanic
flushed intake with antyfire spray and she was dead.

After she hit the ground, everything is clear to me, not in that
moment, but after, she lost fenestron, and she is mad. What I'm
interested in is why she started to setteled down, and why she
wouldn't stop when I pulled colective?
Student said to me that she saw 2-3 minuts before that we were at about
60 percent torq in hover at about 3-4 meters, then, slowly, after some
time she was at about 2-2.5 meters, without him touching the colective,
then he corected her to previus altitude, but hadn't checked the
torq. I didn't cought this, saw it, but thoat he was moving the
colective, trying to establish the altitude, but didn't quite guesing
it right. Whel, after this, I'm thinking.
1.
Ok, the engine was runing on idle, but what if the guvernor was bad in
terms of keeping her operating (43500) rpms, and she is slowly, slowly
trying to reduce rpms. Keep in minde that the student is just started
to learning to hover, so, there is a lot of erors in yaw, altitude,
attitude, but stil in reasonable range, until that aprox 10 degree up
position. So, she is slowly loosing rpm (there's no low rpm warning
horn nor light), and there's no noticable change in engine sound.
Now, she is slowly settling down, student sees it and pull her up
again, reducing the rpm even more. Now, the lift is going with the
square of the speed, and also, with reducing rpm, there is increase in
rotor conning, and reduction in effective rotor surface, so, she is
bleeding her rpms up, to the point, where this becomes more in
deficite, regarding it is not gradual, linear loss. Then, after my
reaction (can figure that nose up, could be student's eror, or...?),
she's starting to go down, and, now there is reduction in inductive
airflow becose the choper is going down, and she's going even more
down. I'm pulling the colective very strong, and, blades are already
critical, this kills them totally, we're banging down and that's
it.
2.
we found that one of the rods wich controls the blade angle (red one)
is broken. If it didn't broke after we hit the ground, maybe that
could explain that nose up angle and down movement. When we shoot off
servo, the colective is going to 8 degrees, maybe she has gone too
after rod broke, and the chopper was left with two thirds of lift with
same weight to support. It's going down. But, aldough there is
balance in mass, there is no way balance in aerodynamic forces now, and
she fell down pretty calm. But then again, the blade with broken rod is
in best condition ine regards to the other two, so...

whell, that's what came to me, so, if somebody has some other idea,
please let me know.
Thanks in advance,

Darko

"mazzonni" wrote in message
oups.com...
Hi to all!
SNIP
... the blade with broken rod is
in best condition ine regards to the other two, so...


Were a Pitch change rod to break, the head would immediately be VERY out of
track. So you would have noticed a very bad one per rev vertical vibration.

Gradual loss of power in a Turbomeca Astazou engine? - Broken spring in
governor bypass. The RPM drops with power but recovers when power is
reduced.

Gradual loss of Main Rotor RPM with no change in engine RPM - Clutch
slipping.

Slatts

Were a Pitch change rod to break, the head would immediately be VERY out of
track. So you would have noticed a very bad one per rev vertical vibration.

yes, i think so too, there was no bad vibrations

Gradual loss of power in a Turbomeca Astazou engine? - Broken spring in
governor bypass. The RPM drops with power but recovers when power is
reduced.

this seems like the cause, hell, should've let her settle slowly down,
but hay, she was going down fast, and left hand just wouldn't stand
still.anyway, that's her



and me, the same night, doctor told me to rest, but, hay, i needed to
celebrate




anyone some other ideas?

thanks, and be safe

darko