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Loud Pop/Hard Landing?


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#1 Nicole-

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Posted 12 January 2019 - 13:55

New to this forum, seems to have a lot of experienced individuals. Im a new CFI (300+hrs), teaching in an 84 R22 Alpha, and was flying with a student. We were in an 8-10ft hover, (regulation hover height at that specific airport) on the taxiway, about to depart, heard a loud pop (deep pop sound, just once, almost sounded like we lost a belt maybe. Deeper than backfire. We were at a small airport, they didnt hear it inside the FBO), took the controls from my student, there was a shudder that lasted until we were on the ground (lateral shudder, like losing a mag, but more so), Started descending a bit, RPMs varied, but didnt lose power. I lowered the collective to get us to the ground and raised it to cushion the landing as we were coming in pretty fast, but that didnt help cushion the landing really at all. Let me clarify, I didnt chop the throttle and enter a hovering auto, we still had engine RPM and rotor RPM, but raising the collective didnt help. When we were on the ground, the throttle was a bit sticky when trying to roll it off, got it down after about 30 seconds or less, no warning lights ever came on, gauges were all fine, didnt over speed or over torque it, minimal carb heat was applied to get it out of the yellow prior to take off, no yaw, landed it level. I gave the controls to my student with the engine running so I could hop out and see if I could hear or see anything. Didnt hit anything, wasnt a plastic bag, bird, etc, belts were all fine, no leaks, no smoke, no smells. I picked it up into a very low hover to get it back to the heli pad and it felt completely normal. My boss drove out and looked it over, everything was as it should be (except that I bent the cross tubes on landing. No further damage). He flew it back the 1hr 40min flight after removing panels, checking controls, checking mags, hovering for about 30mins... and it was perfectly fine. Its being torn apart for the 100hr as well as to inspect everything thoroughly. Has anyone had this happen in the past? Any thoughts on what may have caused this?

#2 Eric Hunt

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Posted 14 January 2019 - 18:46

First thought was a plastic bag, pops when you hit it, laterals while it is still on the blade, and after you bumped into the earth, maybe it came off and blew away before you saw it?

 

I have had one on a blade and it makes an awful noise whizzing around.


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#3 iChris

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Posted 20 January 2019 - 18:58

I’m a new CFI (300+hrs), teaching in an 84 R22 Alpha, and was flying with a student.

 

We were in an 8-10ft hover, (regulation hover height at that specific airport) on the taxiway, about to depart, heard a loud pop (deep pop sound, just once, almost sounded like we lost a belt maybe.

 

Took the controls from my student, there was a shudder that lasted until we were on the ground (lateral shudder, like losing a mag, but more so), Started descending a bit, RPMs varied, but didn’t lose power.

 

I lowered the collective to get us to the ground and raised it to cushion the landing as we were coming in pretty fast, but that didn’t help cushion the landing really at all. Let me clarify, I didn’t chop the throttle and enter a hovering auto, we still had engine RPM and rotor RPM, but raising the collective didn’t help.

 

Got it down after about 30 seconds or less, no warning lights ever came on, gauges were all fine, didn’t over speed or over torque it, minimal carb heat was applied to get it out of the yellow prior to take off, no yaw, landed it level.

 

I picked it up into a very low hover to get it back to the heli-pad and it felt completely normal.

 

My boss drove out and looked it over, everything was as it should be (except that I bent the cross tubes on landing. No further damage). 

 

Any thoughts on what may have caused this? 

 

You took the controls and started descending a bit, RPM varied, but didn’t lose power. If the helicopter was already descending a bit with power, why the rush to lower more collective?  That led to that “pretty fast” decent that required an abrupt up collective at the bottom seconds later, that the R22 could not react to. That hard landing maybe partly your fault regardless of whatever else they find wrong.

 

Sometime it’s better to think momentarily and do the right thing, then to rush or panic and do the wrong thing. I recall the incident of an engine out warning & horn, were the pilot pops the floats completes an autorotation to the water; however the engine was still running. It was an engine out warning system failure, the pilot never verify the other engine power indications. Or the times single engine failure on twin-engine helicopters has led to the pilot rushing and shutting down the good engine. Or even blade contact with an airborne plastic bag, causing a loud pop, as in Eric’s post above.  

 

It’s not clear whether you were in the hover or on the takeoff roll. Fly the helicopter, whatever the case being, the “pop” was the one and only indication of a problem with no other indicators, just calmly and smoothly lower the helicopter to the ground or just let it settle to the ground, no abrupt collective or other control inputs required.

 

 

Buffalo, Wyoming, United States, Mar 2001 NTSB occurrence report: DEN01LA067 

 

Approximately 20 minutes after takeoff on a cross-country flight, the pilot noticed the clutch light was on and he smelled burning rubber. The pilot conducted a power on autorotation and at approximately 50 ft AGL a loud ‘pop’ was heard and the aircraft ‘dropped’ to the ground. Inspection revealed that the upper clutch bearing had failed. A Robinson Safety Notice (#28) requires the pilot to listen during start up and shut down for unusual noises in the upper and lower clutch actuator bearings. According to the safety notice a failed bearing will produce a whine, rumble, growl or siren sound. 

The probable cause of the accident was determined as the failure of the rotor drive system clutch assembly which rendered the aircraft uncontrollable. 

 

Safety Notice SN-28

Issued: Jul 1988 Rev: Jul 2012

LISTEN FOR IMPENDING BEARING FAILURE

 

An impending ball or roller bearing failure is usually preceded by a noticeable increase in noise. The noise will typically start several hours before the bearing actually fails or before there is any increase in bearing temperature. To detect pending failure of a drive system bearing, the pilot should uncover one ear and listen to the sound of the drive system during start-up and shutdown. After the pilot becomes familiar with the normal sound of the drive system, he should be able to detect the noise made by a failing bearing. The failing bearing will produce a loud whine, rumble, growl, or siren sound. Upon hearing an unusual noise, the pilot must immediately ground the aircraft and have the bearings thoroughly inspected by a qualified mechanic. Failure of a bearing in flight could result in a serious accident. 

 

Do not rely on Telatemps to indicate impending bearing failure. A failing bearing may not run hot enough to black out the Telatemps until it actually starts to disintegrate. This may occur only seconds before complete failure.

 

Occasional failures of the upper and lower V-Belt actuator bearings still occur. Undetected failure of these bearings could lead to a power loss and result in a serious accident.   REF: SERVICE BULLETIN #58

 


Edited by iChris, 25 January 2019 - 18:18.

Regards,

Chris

#4 Hand_Grenade_Pilot

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Posted 20 January 2019 - 23:15

New to this forum, seems to have a lot of experienced individuals. Im a new CFI (300+hrs), teaching in an 84 R22 Alpha, and was flying with a student. We were in an 8-10ft hover, (regulation hover height at that specific airport) on the taxiway, about to depart, heard a loud pop (deep pop sound, just once, almost sounded like we lost a belt maybe. Deeper than backfire. We were at a small airport, they didnt hear it inside the FBO), took the controls from my student, there was a shudder that lasted until we were on the ground (lateral shudder, like losing a mag, but more so), Started descending a bit, RPMs varied, but didnt lose power. I lowered the collective to get us to the ground and raised it to cushion the landing as we were coming in pretty fast, but that didnt help cushion the landing really at all. Let me clarify, I didnt chop the throttle and enter a hovering auto, we still had engine RPM and rotor RPM, but raising the collective didnt help. When we were on the ground, the throttle was a bit sticky when trying to roll it off, got it down after about 30 seconds or less, no warning lights ever came on, gauges were all fine, didnt over speed or over torque it, minimal carb heat was applied to get it out of the yellow prior to take off, no yaw, landed it level. I gave the controls to my student with the engine running so I could hop out and see if I could hear or see anything. Didnt hit anything, wasnt a plastic bag, bird, etc, belts were all fine, no leaks, no smoke, no smells. I picked it up into a very low hover to get it back to the heli pad and it felt completely normal. My boss drove out and looked it over, everything was as it should be (except that I bent the cross tubes on landing. No further damage). He flew it back the 1hr 40min flight after removing panels, checking controls, checking mags, hovering for about 30mins... and it was perfectly fine. Its being torn apart for the 100hr as well as to inspect everything thoroughly. Has anyone had this happen in the past? Any thoughts on what may have caused this?


After the loud pop, you mentioned that RPM varied. In what way? Also, do you recall hearing the low RPM horn at all while descending? Was there any yaw movement?
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#5 Scarab

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Posted 21 January 2019 - 12:17

Some years ago a pilot in Arkansas told a story about snagging a plastic bag on his rotorway as he was picking up.  The off balance and drag caused him to wreck it.  No wonder they call those bags "Witches Britches"


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#6 WolftalonID

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Posted 01 February 2019 - 08:39

I saw it happen when I was instructing. Made a pretty loud pop on the bird next to me..we were both running up on the ground. Bag hit so hard it melted slightly to the blades.
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