okrad
19th Dec 2005, 12:24
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
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