R22 Occurrence at Biggin Hill
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R22 Occurrence at Biggin Hill
Apparently 10 days or so ago a R22 made a precautionary landing at Biggin Hill and after shutdown a crack was found in the blade pocket from the training edge forward to the spar, about one third of span out from the root. I've seen a photograph: quite horrifying!
Very surprising that there's been no indication or discussion of this incident here. Or have I missed it?
Very surprising that there's been no indication or discussion of this incident here. Or have I missed it?
Iconoclast
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Blade crack.
IAD05WA016
On November 15, 2004, at 1400 coordinated universal time, a Robinson R-22B, G-DERB, was substantially damaged during landing at Biggin Hill Airfield (EGKB), United Kingdom. The pilot and passenger were not injured.
According to the Air Accidents Investigation Branch (AAIB), the helicopter landed without incident. However, the pilot noticed a vibration after transitioning to a hover at EGKB.
A post flight inspection of the main rotor system revealed that a main rotor blade exhibited a crack, which extended chordwise from the trailing edge, through 75 percent of the chord. In addition, the teeter head was extremely stiff.
This investigation is under jurisdiction of the AAIB. Any further information pertaining to this accident may be obtained from:
Air Accidents Investigation Branch
Berkshire Copse Road
Aldershot
Hampshire GU11 2HH
United Kingdom
This report is for informational purposes and contains only information released by the Government of the United Kingdom.
On November 15, 2004, at 1400 coordinated universal time, a Robinson R-22B, G-DERB, was substantially damaged during landing at Biggin Hill Airfield (EGKB), United Kingdom. The pilot and passenger were not injured.
According to the Air Accidents Investigation Branch (AAIB), the helicopter landed without incident. However, the pilot noticed a vibration after transitioning to a hover at EGKB.
A post flight inspection of the main rotor system revealed that a main rotor blade exhibited a crack, which extended chordwise from the trailing edge, through 75 percent of the chord. In addition, the teeter head was extremely stiff.
This investigation is under jurisdiction of the AAIB. Any further information pertaining to this accident may be obtained from:
Air Accidents Investigation Branch
Berkshire Copse Road
Aldershot
Hampshire GU11 2HH
United Kingdom
This report is for informational purposes and contains only information released by the Government of the United Kingdom.
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If anyone outhere is interested in the original thread regarding the R22 blade, I just happened to be in the hangar when the head and blades were being removed from the helicopter. Let me know if this is still of interest to anyone.
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Heliport,
I have no problem recounting what was found on the disassembly of the R22, but I think I will let the girls calm down a bit otherwise it may get lost in their ranting. (Three posts, nothing to do with the initial thread in the last hour) As it appears that the R22 design was not at fault I think that it is important that we either start a new thread to discuss this or get back to the original discussion. As it takes me ages to type any of this I do not want it lost in the middle of a squabble (No offence intended to the Gods involved)
I have no problem recounting what was found on the disassembly of the R22, but I think I will let the girls calm down a bit otherwise it may get lost in their ranting. (Three posts, nothing to do with the initial thread in the last hour) As it appears that the R22 design was not at fault I think that it is important that we either start a new thread to discuss this or get back to the original discussion. As it takes me ages to type any of this I do not want it lost in the middle of a squabble (No offence intended to the Gods involved)
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Robinson Helicopter Company Issues R-22 Safety Alert
In response to a recent accident involving a rotor blade separation in a Robinson R-22 aircraft, Robinson Helicopter Company has issued a Safety Alert dated December 1, 2004:
Robinson Helicopter Company
(edited to include RHC link - B.B.)
Thanks for posting this.
Despite the link in the last para, the notice hasn't been put on the RHC site yet. I've posted it below for information.
Heliport
Robinson Helicopter Company
(edited to include RHC link - B.B.)
Thanks for posting this.
Despite the link in the last para, the notice hasn't been put on the RHC site yet. I've posted it below for information.
Heliport
In response to a recent accident involving a rotor blade separation in a Robinson R-22 aircraft, Robinson Helicopter Company has issued a Safety Alert dated December 1, 2004:
R-22 Safety Alert: Exceeding Manifold Pressure Limits Can Cause Blade Failure. An A016-2 main rotor blade failure recently occurred at only 700 hours time in service. Although R-22 blades have a 2,200 hour service life, repeated over-stressing can substantially reduce blade fatigue life. Exceeding manifold pressure limits produces excessive stress and can result in premature fatigue failure.
Warning:
1) If the helicopter has been occassionally operated above manifold pressure limits, replace main rotor blades.
2) If the helicopter is normally parked outside in humid climates, particularly in tropical or coastal areas, replace A016-2 main rotor blades prior to 5 years time in service due to possible internal corrosion.
3) If main rotor vibration increases during flight, make an immediate safe landing and determine the cause of vibration before further flight. If cause cannot be determined, replace main rotor blades before further flight.
Operators are also reminded to reread Safety Notices SN-37 and SN-39. Safety Notice 37, "Exceeding Approved Limitations Can Be Fatal" was issued on December 1, 2001. Safety Notice 39, "Unusual Vibration Can Indicate A Main Rotor Blade Crack" was issued in July 2003. These Safety Notices can be viewed at Robinson Company web site.
R-22 Safety Alert: Exceeding Manifold Pressure Limits Can Cause Blade Failure. An A016-2 main rotor blade failure recently occurred at only 700 hours time in service. Although R-22 blades have a 2,200 hour service life, repeated over-stressing can substantially reduce blade fatigue life. Exceeding manifold pressure limits produces excessive stress and can result in premature fatigue failure.
Warning:
1) If the helicopter has been occassionally operated above manifold pressure limits, replace main rotor blades.
2) If the helicopter is normally parked outside in humid climates, particularly in tropical or coastal areas, replace A016-2 main rotor blades prior to 5 years time in service due to possible internal corrosion.
3) If main rotor vibration increases during flight, make an immediate safe landing and determine the cause of vibration before further flight. If cause cannot be determined, replace main rotor blades before further flight.
Operators are also reminded to reread Safety Notices SN-37 and SN-39. Safety Notice 37, "Exceeding Approved Limitations Can Be Fatal" was issued on December 1, 2001. Safety Notice 39, "Unusual Vibration Can Indicate A Main Rotor Blade Crack" was issued in July 2003. These Safety Notices can be viewed at Robinson Company web site.
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Nice to see this thread back on track
Before we start I would like to say that I am a pilot and not a helicopter engineer, but this post has been written in conjunction with the engineer that disassembled the aircraft. I have described what was found. The A.A.I.B. were present and I am sure that a full report will be published in the future. From my own point of view I have a few hours on the R22 and therefore have an interest in the continued airworthiness of the type. Nothing I saw gave me any concern about the design of the aircraft and it is a testament to the strength of the blade design that it had remained intact.
The helicopter in question landed at Biggin Hill airport with a vibration. The local maintenance company (Not the company responsible for the maintenance of the aircraft) were asked to investigate the problem. On initial investigation it was discovered that there was a crack from the trailing edge of the blade to just before the “D” section at the leading edge of the blade approximately one third of the span from the root. The crack was through both top and bottom skins and the honeycomb. It was noted that the rotor head was unable to flap about the teetering hinge. The blades were removed from the aircraft and then the head was removed. During the disassembly of the rotor head it became very clear that the head was unable to teeter. The head was then stripped and it was discovered that the shims that are required to be fitted in-between the surface of the rotor head and the thrust washers were absent. In my humble opinion it would seem that since the head was unable to teeter the rotor blade had to take the stresses that teetering would normally allow and therefore the crack developed.
They were very lucky.
Before we start I would like to say that I am a pilot and not a helicopter engineer, but this post has been written in conjunction with the engineer that disassembled the aircraft. I have described what was found. The A.A.I.B. were present and I am sure that a full report will be published in the future. From my own point of view I have a few hours on the R22 and therefore have an interest in the continued airworthiness of the type. Nothing I saw gave me any concern about the design of the aircraft and it is a testament to the strength of the blade design that it had remained intact.
The helicopter in question landed at Biggin Hill airport with a vibration. The local maintenance company (Not the company responsible for the maintenance of the aircraft) were asked to investigate the problem. On initial investigation it was discovered that there was a crack from the trailing edge of the blade to just before the “D” section at the leading edge of the blade approximately one third of the span from the root. The crack was through both top and bottom skins and the honeycomb. It was noted that the rotor head was unable to flap about the teetering hinge. The blades were removed from the aircraft and then the head was removed. During the disassembly of the rotor head it became very clear that the head was unable to teeter. The head was then stripped and it was discovered that the shims that are required to be fitted in-between the surface of the rotor head and the thrust washers were absent. In my humble opinion it would seem that since the head was unable to teeter the rotor blade had to take the stresses that teetering would normally allow and therefore the crack developed.
They were very lucky.
PPRuNe Enigma
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It was noted that the rotor head was unable to flap about the teetering hinge.
An instructor once asked me why ? - since it's not on the checklist. Sounds like this incident gives a pretty good reason for doing so.
I'm gonna keep doing it !
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R22 Occurrence at Biggin Hill
Ed Thrust1V. I would be interested to see more details on the shim/bearing situation. For example. Given as you state, that the shims were missing,and the head was seized, does one assume that the teeter shaft was seized?. If it was seized, was it in the alloy head or the top of the rotor shaft. Did the engineer give any reason as to why the shims were missing (or how, if they were present originally) they managed to remove themselves from the shaft (scoring of the inner face of the alloy head for example) Had the head seized in exactly neutral position. Thanks, Bug.
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I started out on the R22 and was always taught to push up on the blade, partly on the basis that during the pre-flight you check that everything that moves actually moves and everything that is supposed to stay still, stays still!
Helicopter Pilots Get It Up Quicker
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Interesting. As a habit, during a check 'A' I always push up on each blade to check the movement of the flapping and teeter hinges.
PW
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Budgevheli,
I am not sure what you mean by ”was the teeter shaft seized?” I can tell you that the shims had not been fitted. The engineer who disassembled the head was not responsible for the maintenance of the aircraft and had been asked by the A.A.I.B. to investigate. He therefore has no idea why the shims were not present. The head appeared to be perpendicular to the main rotor shaft. I hope this answers your questions. If you have a look at Dave Jackson’s post above the extract from the R22 maintenance manual gives details on how the rotor head should be assembled.
I am not sure what you mean by ”was the teeter shaft seized?” I can tell you that the shims had not been fitted. The engineer who disassembled the head was not responsible for the maintenance of the aircraft and had been asked by the A.A.I.B. to investigate. He therefore has no idea why the shims were not present. The head appeared to be perpendicular to the main rotor shaft. I hope this answers your questions. If you have a look at Dave Jackson’s post above the extract from the R22 maintenance manual gives details on how the rotor head should be assembled.
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R22 Occurrence at Biggin Hill
Ed Thrust 1V. Thanks for the reply. I am interested to find out how, apart from locking the head up solid by overtightening the main teeter head bolt, how the head could be seized especially if the shims were missing. Without the shims I guess the head could be squeezed in and could rub against the sides of the shaft, but the gap seems too large for this to occur as there is sufficient room to move the head across to set the head laterally. As the robinson head relies on a spanner type action of the spacers against the faces of the shaft, I thought it just may be possible to bend the main teeter bolt sufficiently to make it difficult to remove. I have worked on these heads hence my interest. I do not doubt what you stated is correct I am curious as to how it can occur. Many Thanks Bug.
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Technical - but on subject.
bugdevheli,
The bearing is a flanged bushing [see Tuflite Bearings] . The shims are located between the journals and the thrust washers. The addition of shims causes the friction between the non-teetering thrust washers and the flanges on the bearing to be reduced.
The above better be correct, because I'm waiting for a quote right now on these bearings for the Constant Velocity Joint w/ Hub Spring Rotor.
Dave J.
The bearing is a flanged bushing [see Tuflite Bearings] . The shims are located between the journals and the thrust washers. The addition of shims causes the friction between the non-teetering thrust washers and the flanges on the bearing to be reduced.
The above better be correct, because I'm waiting for a quote right now on these bearings for the Constant Velocity Joint w/ Hub Spring Rotor.
Dave J.
