R44 inflight breakup story - TV NZ
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This is as close to RHC has got to recording a rotor divergence accident - it’s audio only and from 1992 so 30 years ago. Rotor head design exactly the same then as it is now. Seemingly no control inputs from instructor or student and in level cruise flight when it occurred (no low RPM horn etc either). Reproduced from an article headlined Undetermined Reasons in Vertical October 2016.
On June 29, 1992, a flight instructor and his pre-solo student took to the air in a Robinson R22 helicopter over northern California’s San Francisco Bay Area. The instructor was relatively experienced, with about 2,000 hours of R22 flight time. The student had only four hours of flight time, all in the R22. She had brought along a microcassette voice recorder, which was set up to tape the cockpit and radio communications during her lesson.
The helicopter’s low rotor r.p.m. warning horn was checked on the ground before takeoff; it operated normally. And nothing appeared to be out of the ordinary during the 17-minute flight to a local practice area near Richmond, where the student, at the instructor’s request, executed a shallow left turn.
The U.S. National Transportation Safety Board (NTSB) described what happened next: “Seconds later, while cruising at 2,200 feet, the CFI [certified flight instructor] began talking. In mid-sentence an undetermined event occurred which interrupted his speech. A wind-like background noise started, and the student exclaimed, ‘Help.'”
Radar data confirmed witness reports that the helicopter’s tail boom and main rotor had separated in level flight. The aircraft plunged into the San Pablo Bay, killing the instructor and student. Examination of the wreckage revealed that the aircraft had experienced “mast bumping” — severe contact of the rotor hubs with the mast, a phenomenon that is often associated with low-G maneuvering. The main rotor blades had diverged to strike the tail boom, which can occur as a result of mast bumping or low r.p.m., leading to rotor stall.
Before the Richmond crash, 23 other Robinson R22s had experienced similar losses of main rotor control — events which are almost always fatal and, in the absence of recording devices, leave few clues as to their causes. Investigators trying to piece together circumstances after the fact had chalked up many of these accidents to low-G maneuvering or low rotor r.p.m., implying mishandling by the pilot.
But the recorded evidence in the Richmond crash simply didn’t support the usual explanations. Neither pilot had voiced any concern about the operation of the helicopter before the breakup. The low r.p.m. warning horn didn’t activate before or during the breakup sequence, and spectral analysis of the audiotape indicated that the aircraft was being operated at a normal main rotor r.p.m. Radar data showed that the airspeed was normal for cruise flight, and there was nothing to suggest low-G maneuvering.
With no easy way to explain the Richmond crash, the NTSB launched a special investigation into R22 loss of main rotor control accidents. Meanwhile, the U.S. Federal Aviation Administration (FAA), which had already conducted two special certification reviews of the R22, initiated a third. It also convened a technical panel to study R22 loss of main rotor control accidents, and commissioned the Georgia Institute of Technology (Georgia Tech) to conduct simulation studies of the R22 main rotor system.
In addition to several airworthiness directives and bulletins, in February 1995, the FAA issued Special Federal Aviation Regulation (SFAR) 73, which created specific training and proficiency requirements for Robinson R22 and R44 helicopters. When the NTSB issued its own special investigation report the following year, it was still unable to explain the Richmond crash and many similar accidents, but it was encouraged by the fact that no loss of main rotor control accidents had occurred since the SFAR was enacted.
Although the Safety Board cannot conclude that the operational changes will eliminate all in-flight rotor strikes, the absence of such accidents since these actions were implemented suggests that they have been effective,” the NTSB wrote. “The absence of such accidents also supports the proposition that most of the accidents were caused by large, abrupt control inputs and the corrective actions taken should help prevent such accidents.”
Since SFAR 73 was enacted, Robinson loss of main rotor control accidents have occurred less frequently in the U.S., but they haven’t stopped entirely. And in at least one country, New Zealand, they have continued to occur at a high rate, with New Zealand’s Transport Accident Investigation Commission (TAIC) citing at least 12 such accidents or incidents since 1996, despite the relatively low total number of Robinson helicopters in the country.
In a very small number of these accidents, there is eyewitness testimony or other direct evidence to suggest improper handling by the pilot. But in most cases, investigators are no closer to being able to explain these accidents than they were 20 years ago. For almost all of them, the probable cause statements are essentially the same: “the divergence of the main rotor from its normal plane of rotation for an undetermined reason.”
On June 29, 1992, a flight instructor and his pre-solo student took to the air in a Robinson R22 helicopter over northern California’s San Francisco Bay Area. The instructor was relatively experienced, with about 2,000 hours of R22 flight time. The student had only four hours of flight time, all in the R22. She had brought along a microcassette voice recorder, which was set up to tape the cockpit and radio communications during her lesson.
The helicopter’s low rotor r.p.m. warning horn was checked on the ground before takeoff; it operated normally. And nothing appeared to be out of the ordinary during the 17-minute flight to a local practice area near Richmond, where the student, at the instructor’s request, executed a shallow left turn.
The U.S. National Transportation Safety Board (NTSB) described what happened next: “Seconds later, while cruising at 2,200 feet, the CFI [certified flight instructor] began talking. In mid-sentence an undetermined event occurred which interrupted his speech. A wind-like background noise started, and the student exclaimed, ‘Help.'”
Radar data confirmed witness reports that the helicopter’s tail boom and main rotor had separated in level flight. The aircraft plunged into the San Pablo Bay, killing the instructor and student. Examination of the wreckage revealed that the aircraft had experienced “mast bumping” — severe contact of the rotor hubs with the mast, a phenomenon that is often associated with low-G maneuvering. The main rotor blades had diverged to strike the tail boom, which can occur as a result of mast bumping or low r.p.m., leading to rotor stall.
Before the Richmond crash, 23 other Robinson R22s had experienced similar losses of main rotor control — events which are almost always fatal and, in the absence of recording devices, leave few clues as to their causes. Investigators trying to piece together circumstances after the fact had chalked up many of these accidents to low-G maneuvering or low rotor r.p.m., implying mishandling by the pilot.
But the recorded evidence in the Richmond crash simply didn’t support the usual explanations. Neither pilot had voiced any concern about the operation of the helicopter before the breakup. The low r.p.m. warning horn didn’t activate before or during the breakup sequence, and spectral analysis of the audiotape indicated that the aircraft was being operated at a normal main rotor r.p.m. Radar data showed that the airspeed was normal for cruise flight, and there was nothing to suggest low-G maneuvering.
With no easy way to explain the Richmond crash, the NTSB launched a special investigation into R22 loss of main rotor control accidents. Meanwhile, the U.S. Federal Aviation Administration (FAA), which had already conducted two special certification reviews of the R22, initiated a third. It also convened a technical panel to study R22 loss of main rotor control accidents, and commissioned the Georgia Institute of Technology (Georgia Tech) to conduct simulation studies of the R22 main rotor system.
In addition to several airworthiness directives and bulletins, in February 1995, the FAA issued Special Federal Aviation Regulation (SFAR) 73, which created specific training and proficiency requirements for Robinson R22 and R44 helicopters. When the NTSB issued its own special investigation report the following year, it was still unable to explain the Richmond crash and many similar accidents, but it was encouraged by the fact that no loss of main rotor control accidents had occurred since the SFAR was enacted.
Although the Safety Board cannot conclude that the operational changes will eliminate all in-flight rotor strikes, the absence of such accidents since these actions were implemented suggests that they have been effective,” the NTSB wrote. “The absence of such accidents also supports the proposition that most of the accidents were caused by large, abrupt control inputs and the corrective actions taken should help prevent such accidents.”
Since SFAR 73 was enacted, Robinson loss of main rotor control accidents have occurred less frequently in the U.S., but they haven’t stopped entirely. And in at least one country, New Zealand, they have continued to occur at a high rate, with New Zealand’s Transport Accident Investigation Commission (TAIC) citing at least 12 such accidents or incidents since 1996, despite the relatively low total number of Robinson helicopters in the country.
In a very small number of these accidents, there is eyewitness testimony or other direct evidence to suggest improper handling by the pilot. But in most cases, investigators are no closer to being able to explain these accidents than they were 20 years ago. For almost all of them, the probable cause statements are essentially the same: “the divergence of the main rotor from its normal plane of rotation for an undetermined reason.”
This is as close to RHC has got to recording a rotor divergence accident - it’s audio only and from 1992 so 30 years ago. Rotor head design exactly the same then as it is now. Seemingly no control inputs from instructor or student and in level cruise flight when it occurred (no low RPM horn etc either). Reproduced from an article headlined Undetermined Reasons in Vertical October 2016.
On June 29, 1992, a flight instructor and his pre-solo student took to the air in a Robinson R22 helicopter over northern California’s San Francisco Bay Area. The instructor was relatively experienced, with about 2,000 hours of R22 flight time. The student had only four hours of flight time, all in the R22. She had brought along a microcassette voice recorder, which was set up to tape the cockpit and radio communications during her lesson.
The helicopter’s low rotor r.p.m. warning horn was checked on the ground before takeoff; it operated normally. And nothing appeared to be out of the ordinary during the 17-minute flight to a local practice area near Richmond, where the student, at the instructor’s request, executed a shallow left turn.
The U.S. National Transportation Safety Board (NTSB) described what happened next: “Seconds later, while cruising at 2,200 feet, the CFI [certified flight instructor] began talking. In mid-sentence an undetermined event occurred which interrupted his speech. A wind-like background noise started, and the student exclaimed, ‘Help.'”
Radar data confirmed witness reports that the helicopter’s tail boom and main rotor had separated in level flight. The aircraft plunged into the San Pablo Bay, killing the instructor and student. Examination of the wreckage revealed that the aircraft had experienced “mast bumping” — severe contact of the rotor hubs with the mast, a phenomenon that is often associated with low-G maneuvering. The main rotor blades had diverged to strike the tail boom, which can occur as a result of mast bumping or low r.p.m., leading to rotor stall.
...
Since SFAR 73 was enacted, Robinson loss of main rotor control accidents have occurred less frequently in the U.S., but they haven’t stopped entirely. And in at least one country, New Zealand, they have continued to occur at a high rate, with New Zealand’s Transport Accident Investigation Commission (TAIC) citing at least 12 such accidents or incidents since 1996, despite the relatively low total number of Robinson helicopters in the country.
In a very small number of these accidents, there is eyewitness testimony or other direct evidence to suggest improper handling by the pilot. But in most cases, investigators are no closer to being able to explain these accidents than they were 20 years ago. For almost all of them, the probable cause statements are essentially the same: “the divergence of the main rotor from its normal plane of rotation for an undetermined reason.”
On June 29, 1992, a flight instructor and his pre-solo student took to the air in a Robinson R22 helicopter over northern California’s San Francisco Bay Area. The instructor was relatively experienced, with about 2,000 hours of R22 flight time. The student had only four hours of flight time, all in the R22. She had brought along a microcassette voice recorder, which was set up to tape the cockpit and radio communications during her lesson.
The helicopter’s low rotor r.p.m. warning horn was checked on the ground before takeoff; it operated normally. And nothing appeared to be out of the ordinary during the 17-minute flight to a local practice area near Richmond, where the student, at the instructor’s request, executed a shallow left turn.
The U.S. National Transportation Safety Board (NTSB) described what happened next: “Seconds later, while cruising at 2,200 feet, the CFI [certified flight instructor] began talking. In mid-sentence an undetermined event occurred which interrupted his speech. A wind-like background noise started, and the student exclaimed, ‘Help.'”
Radar data confirmed witness reports that the helicopter’s tail boom and main rotor had separated in level flight. The aircraft plunged into the San Pablo Bay, killing the instructor and student. Examination of the wreckage revealed that the aircraft had experienced “mast bumping” — severe contact of the rotor hubs with the mast, a phenomenon that is often associated with low-G maneuvering. The main rotor blades had diverged to strike the tail boom, which can occur as a result of mast bumping or low r.p.m., leading to rotor stall.
...
Since SFAR 73 was enacted, Robinson loss of main rotor control accidents have occurred less frequently in the U.S., but they haven’t stopped entirely. And in at least one country, New Zealand, they have continued to occur at a high rate, with New Zealand’s Transport Accident Investigation Commission (TAIC) citing at least 12 such accidents or incidents since 1996, despite the relatively low total number of Robinson helicopters in the country.
In a very small number of these accidents, there is eyewitness testimony or other direct evidence to suggest improper handling by the pilot. But in most cases, investigators are no closer to being able to explain these accidents than they were 20 years ago. For almost all of them, the probable cause statements are essentially the same: “the divergence of the main rotor from its normal plane of rotation for an undetermined reason.”
This is as close to RHC has got to recording a rotor divergence accident - it’s audio only and from 1992 so 30 years ago. Rotor head design exactly the same then as it is now. Seemingly no control inputs from instructor or student and in level cruise flight when it occurred (no low RPM horn etc either). Reproduced from an article headlined Undetermined Reasons in Vertical October 2016.
On June 29, 1992, a flight instructor and his pre-solo student took to the air in a Robinson R22 helicopter over northern California’s San Francisco Bay Area. The instructor was relatively experienced, with about 2,000 hours of R22 flight time. The student had only four hours of flight time, all in the R22. She had brought along a microcassette voice recorder, which was set up to tape the cockpit and radio communications during her lesson.
The helicopter’s low rotor r.p.m. warning horn was checked on the ground before takeoff; it operated normally. And nothing appeared to be out of the ordinary during the 17-minute flight to a local practice area near Richmond, where the student, at the instructor’s request, executed a shallow left turn.
The U.S. National Transportation Safety Board (NTSB) described what happened next: “Seconds later, while cruising at 2,200 feet, the CFI [certified flight instructor] began talking. In mid-sentence an undetermined event occurred which interrupted his speech. A wind-like background noise started, and the student exclaimed, ‘Help.'”
Radar data confirmed witness reports that the helicopter’s tail boom and main rotor had separated in level flight. The aircraft plunged into the San Pablo Bay, killing the instructor and student. Examination of the wreckage revealed that the aircraft had experienced “mast bumping” — severe contact of the rotor hubs with the mast, a phenomenon that is often associated with low-G maneuvering. The main rotor blades had diverged to strike the tail boom, which can occur as a result of mast bumping or low r.p.m., leading to rotor stall.
Before the Richmond crash, 23 other Robinson R22s had experienced similar losses of main rotor control — events which are almost always fatal and, in the absence of recording devices, leave few clues as to their causes. Investigators trying to piece together circumstances after the fact had chalked up many of these accidents to low-G maneuvering or low rotor r.p.m., implying mishandling by the pilot.
But the recorded evidence in the Richmond crash simply didn’t support the usual explanations. Neither pilot had voiced any concern about the operation of the helicopter before the breakup. The low r.p.m. warning horn didn’t activate before or during the breakup sequence, and spectral analysis of the audiotape indicated that the aircraft was being operated at a normal main rotor r.p.m. Radar data showed that the airspeed was normal for cruise flight, and there was nothing to suggest low-G maneuvering.
On June 29, 1992, a flight instructor and his pre-solo student took to the air in a Robinson R22 helicopter over northern California’s San Francisco Bay Area. The instructor was relatively experienced, with about 2,000 hours of R22 flight time. The student had only four hours of flight time, all in the R22. She had brought along a microcassette voice recorder, which was set up to tape the cockpit and radio communications during her lesson.
The helicopter’s low rotor r.p.m. warning horn was checked on the ground before takeoff; it operated normally. And nothing appeared to be out of the ordinary during the 17-minute flight to a local practice area near Richmond, where the student, at the instructor’s request, executed a shallow left turn.
The U.S. National Transportation Safety Board (NTSB) described what happened next: “Seconds later, while cruising at 2,200 feet, the CFI [certified flight instructor] began talking. In mid-sentence an undetermined event occurred which interrupted his speech. A wind-like background noise started, and the student exclaimed, ‘Help.'”
Radar data confirmed witness reports that the helicopter’s tail boom and main rotor had separated in level flight. The aircraft plunged into the San Pablo Bay, killing the instructor and student. Examination of the wreckage revealed that the aircraft had experienced “mast bumping” — severe contact of the rotor hubs with the mast, a phenomenon that is often associated with low-G maneuvering. The main rotor blades had diverged to strike the tail boom, which can occur as a result of mast bumping or low r.p.m., leading to rotor stall.
Before the Richmond crash, 23 other Robinson R22s had experienced similar losses of main rotor control — events which are almost always fatal and, in the absence of recording devices, leave few clues as to their causes. Investigators trying to piece together circumstances after the fact had chalked up many of these accidents to low-G maneuvering or low rotor r.p.m., implying mishandling by the pilot.
But the recorded evidence in the Richmond crash simply didn’t support the usual explanations. Neither pilot had voiced any concern about the operation of the helicopter before the breakup. The low r.p.m. warning horn didn’t activate before or during the breakup sequence, and spectral analysis of the audiotape indicated that the aircraft was being operated at a normal main rotor r.p.m. Radar data showed that the airspeed was normal for cruise flight, and there was nothing to suggest low-G maneuvering.
I sometimes wonder if maybe spacial disorientation had something to do with it, as the water in that bay is so still and glossy that I always had to force myself to not look down, as it would mess me up pretty quick.
You would need to know exactly what the instructor was saying to the student at the time - if he was verbally correcting an error she had made in the turn, it is possible he was on the verge of taking control and that her control inputs had already put them in a hazardous position.
Robbiee - You are correct, it can be very disorientating flying over a glassy sea.
Robbiee - You are correct, it can be very disorientating flying over a glassy sea.
Originally Posted by [email protected]
You would need to know exactly what the instructor was saying to the student at the time - if he was verbally correcting an error she had made in the turn, it is possible he was on the verge of taking control and that her control inputs had already put them in a hazardous position.
It reads as if NTSB didn't have a clue regarding what initiated it even after the investigation
Many thanks for the various explanations re mast bumping etc.. I asked because many years ago, before I was a pilot, I was given an R22 ride as a birthday present. The pilot let me have a bit of a waggle on the controls etc, then did a simulated engine-out auto rotate to a landing. This went well, but knowing what I know now, I would have said "no thanks" to that particular part of the demonstration !!
With all the mast bumping incidents, is it not well overdue for a redesign - strengthening the mast and some sort of soft ring within the teeter head to prevent mast damage from bumping?
With all the mast bumping incidents, is it not well overdue for a redesign - strengthening the mast and some sort of soft ring within the teeter head to prevent mast damage from bumping?
Many thanks for the various explanations re mast bumping etc.. I asked because many years ago, before I was a pilot, I was given an R22 ride as a birthday present. The pilot let me have a bit of a waggle on the controls etc, then did a simulated engine-out auto rotate to a landing. This went well, but knowing what I know now, I would have said "no thanks" to that particular part of the demonstration !!
With all the mast bumping incidents, is it not well overdue for a redesign - strengthening the mast and some sort of soft ring within the teeter head to prevent mast damage from bumping?
With all the mast bumping incidents, is it not well overdue for a redesign - strengthening the mast and some sort of soft ring within the teeter head to prevent mast damage from bumping?
Anyway, better training seems to have eliminated most of these types of accidents here in the States where the R22 is the most common training helicopter. Why they are still happening in New Zealand is beyond me?
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This is from a post about another Robinson accident being discussed on this forum in 2020.
Quote:
Originally Posted by Arnie Madsen View Post
I am not anti-Robinson but we must acknowledge that very light blades are more sensitive to turbulence & mast bumping.
Heavy blades retain their plane of rotation long enough to handle sudden strong gusts.
But they require extra strength (heavy) laminations & spar at the root end to handle bending loads at the root (blade coning)
Frank came up with a good solution to save ounces and pounds in the rotor system
By incorporating coning hinges at the root which relieved any coning stress
Thus he could build very light blades .... which had the additional benefits of lower centrifugal force on the hub and feather bearings which meant he could build a lighter head.
Early blade de-laminations were the first red flag , but were attributed to outsourced blade manufacturing errors
Then came the numerous unexplained rotor incursions into the cabin or boom. A big red flag ... not to mention further de-laminations through the years
Easy for me to say ... but if he (stubborn frank) had halted production , built a blade similar to the H269 , strengthened the hub to take the extra loads , the problem would have been solved.
Of course those several pounds of weight would have reduced payload .... but extra pitch along with extra power from the de-rated engine should solve that ..... working the Lycoming a bit harder would likely reduce TBO from 2200 hrs to 1800 hrs which is still excellent for piston helicopters.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
i replied to this post TTSN
There ... you just hit the nail firmly on the head. In 25 years plus of following Robinson rotor issues this seems to be the view of a number of the worlds experts. The numerous unexplained Robinson rotor divergence issues are unique but so is the rotor head design with a teeter and 2 coning hinges. I’m sure this particular accident was due to being out in the wrong kind of weather and the result would have been the same regardless of what type of light helicopter was being flown. More frequent checks on the condition of the coning bolts and closely monitoring preload (resistance to movement) should be introduced. A Robinson operator told a story on here (PPrune) a couple of years ago of finding the broken off end of his coning bolt during a pre flight check in the hangar (a little alarming I know). I’m not a Robinson hater in any shape or form and would be willing to assist in any way I could reducing or solving this issue.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
Quote:
Originally Posted by Arnie Madsen View Post
I am not anti-Robinson but we must acknowledge that very light blades are more sensitive to turbulence & mast bumping.
Heavy blades retain their plane of rotation long enough to handle sudden strong gusts.
But they require extra strength (heavy) laminations & spar at the root end to handle bending loads at the root (blade coning)
Frank came up with a good solution to save ounces and pounds in the rotor system
By incorporating coning hinges at the root which relieved any coning stress
Thus he could build very light blades .... which had the additional benefits of lower centrifugal force on the hub and feather bearings which meant he could build a lighter head.
Early blade de-laminations were the first red flag , but were attributed to outsourced blade manufacturing errors
Then came the numerous unexplained rotor incursions into the cabin or boom. A big red flag ... not to mention further de-laminations through the years
Easy for me to say ... but if he (stubborn frank) had halted production , built a blade similar to the H269 , strengthened the hub to take the extra loads , the problem would have been solved.
Of course those several pounds of weight would have reduced payload .... but extra pitch along with extra power from the de-rated engine should solve that ..... working the Lycoming a bit harder would likely reduce TBO from 2200 hrs to 1800 hrs which is still excellent for piston helicopters.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
i replied to this post TTSN
There ... you just hit the nail firmly on the head. In 25 years plus of following Robinson rotor issues this seems to be the view of a number of the worlds experts. The numerous unexplained Robinson rotor divergence issues are unique but so is the rotor head design with a teeter and 2 coning hinges. I’m sure this particular accident was due to being out in the wrong kind of weather and the result would have been the same regardless of what type of light helicopter was being flown. More frequent checks on the condition of the coning bolts and closely monitoring preload (resistance to movement) should be introduced. A Robinson operator told a story on here (PPrune) a couple of years ago of finding the broken off end of his coning bolt during a pre flight check in the hangar (a little alarming I know). I’m not a Robinson hater in any shape or form and would be willing to assist in any way I could reducing or solving this issue.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
This is from a post about another Robinson accident being discussed on this forum in 2020.
Quote:
Originally Posted by Arnie Madsen View Post
I am not anti-Robinson but we must acknowledge that very light blades are more sensitive to turbulence & mast bumping.
Heavy blades retain their plane of rotation long enough to handle sudden strong gusts.
But they require extra strength (heavy) laminations & spar at the root end to handle bending loads at the root (blade coning)
Frank came up with a good solution to save ounces and pounds in the rotor system
By incorporating coning hinges at the root which relieved any coning stress
Thus he could build very light blades .... which had the additional benefits of lower centrifugal force on the hub and feather bearings which meant he could build a lighter head.
Early blade de-laminations were the first red flag , but were attributed to outsourced blade manufacturing errors
Then came the numerous unexplained rotor incursions into the cabin or boom. A big red flag ... not to mention further de-laminations through the years
Easy for me to say ... but if he (stubborn frank) had halted production , built a blade similar to the H269 , strengthened the hub to take the extra loads , the problem would have been solved.
Of course those several pounds of weight would have reduced payload .... but extra pitch along with extra power from the de-rated engine should solve that ..... working the Lycoming a bit harder would likely reduce TBO from 2200 hrs to 1800 hrs which is still excellent for piston helicopters.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
i replied to this post TTSN
There ... you just hit the nail firmly on the head. In 25 years plus of following Robinson rotor issues this seems to be the view of a number of the worlds experts. The numerous unexplained Robinson rotor divergence issues are unique but so is the rotor head design with a teeter and 2 coning hinges. I’m sure this particular accident was due to being out in the wrong kind of weather and the result would have been the same regardless of what type of light helicopter was being flown. More frequent checks on the condition of the coning bolts and closely monitoring preload (resistance to movement) should be introduced. A Robinson operator told a story on here (PPrune) a couple of years ago of finding the broken off end of his coning bolt during a pre flight check in the hangar (a little alarming I know). I’m not a Robinson hater in any shape or form and would be willing to assist in any way I could reducing or solving this issue.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
Quote:
Originally Posted by Arnie Madsen View Post
I am not anti-Robinson but we must acknowledge that very light blades are more sensitive to turbulence & mast bumping.
Heavy blades retain their plane of rotation long enough to handle sudden strong gusts.
But they require extra strength (heavy) laminations & spar at the root end to handle bending loads at the root (blade coning)
Frank came up with a good solution to save ounces and pounds in the rotor system
By incorporating coning hinges at the root which relieved any coning stress
Thus he could build very light blades .... which had the additional benefits of lower centrifugal force on the hub and feather bearings which meant he could build a lighter head.
Early blade de-laminations were the first red flag , but were attributed to outsourced blade manufacturing errors
Then came the numerous unexplained rotor incursions into the cabin or boom. A big red flag ... not to mention further de-laminations through the years
Easy for me to say ... but if he (stubborn frank) had halted production , built a blade similar to the H269 , strengthened the hub to take the extra loads , the problem would have been solved.
Of course those several pounds of weight would have reduced payload .... but extra pitch along with extra power from the de-rated engine should solve that ..... working the Lycoming a bit harder would likely reduce TBO from 2200 hrs to 1800 hrs which is still excellent for piston helicopters.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
i replied to this post TTSN
There ... you just hit the nail firmly on the head. In 25 years plus of following Robinson rotor issues this seems to be the view of a number of the worlds experts. The numerous unexplained Robinson rotor divergence issues are unique but so is the rotor head design with a teeter and 2 coning hinges. I’m sure this particular accident was due to being out in the wrong kind of weather and the result would have been the same regardless of what type of light helicopter was being flown. More frequent checks on the condition of the coning bolts and closely monitoring preload (resistance to movement) should be introduced. A Robinson operator told a story on here (PPrune) a couple of years ago of finding the broken off end of his coning bolt during a pre flight check in the hangar (a little alarming I know). I’m not a Robinson hater in any shape or form and would be willing to assist in any way I could reducing or solving this issue.
I am also suspicious of having 3 hinge points on a 2 blade rotor .... if a split second disturbance caused one blade to pivot on a coning hinge it would immediately put everything out of phase and would self-destruct.
Coning hinge... : If the tensions get messed up, it gets ugly very quickly, but not like these cases. Having had a coming hinge fail in flight, it was a rapid progressive ugly, but not instantaneous. I detected the anomaly climbing out over the C-17 building, and did an abbreviated circuit to the grass. Landed. Instructor with me picked up to the hover to get his thoughts and he was visibly being shaken by the cyclic, not something that normally happens. After a discussion he hover taxied back to the lines about 2 minutes and by landing the head was toast. It was progressive, but not instantaneous. The R22 that had one blade shear from the TE to the D cell still took time and that was with a failed coning hinge. Apparently did fly funny. Spectacular photo..
Effect of gusts doesn't have much relationship with blade mass, lock number is affected of course.
Just wasted 7 hrs on a flight re reading Johnson, and can't see that there is a torsion harmonic issue, that would be over 109% NR for the....??? 7th mode??? (It put me to sleep)
Concorde's noted wind noise brings up the thought that a yaw event occurred, but most causes would leave evidence in the blades, hub, control runs.
No question that teeter heads are not happy with low g, but Concorde and Queenstown do not suggest low g from environmental conditions. The comment of disorientation, the bay is often like a milk bottle interior with the haze taking out a distinct horizon, the NTSB not making a comment on that doesn't preclude it as an issue.
The RHC deserves a good evaluation of the rotor head to resolve the matter, it has a place in the industry as a valuable tool
Many thanks for the various explanations re mast bumping etc.. I asked because many years ago, before I was a pilot, I was given an R22 ride as a birthday present. The pilot let me have a bit of a waggle on the controls etc, then did a simulated engine-out auto rotate to a landing. This went well, but knowing what I know now, I would have said "no thanks" to that particular part of the demonstration !!
Then I am afraid you learned the wrong thing over the course of the last twenty odd posts.
Well, I got my license in 1983, 2600 hrs in Robinson and I paid for everyone of them, bought and used and sold 16 r22 and mainly r44 machines, never had an issue, I have always run them hard and fast, but not in mountains. I can see where you could have problems but not in my experience. Flown as dictated by Robinson I think your safe, but I wouldn't buy one to fly around New Zealand or similar mountains. Taking in to account all of what has been said would I fly / buy another? Well yes but I am not real keen on the 22 anymore but happy with the R44.
Thread Starter
https://www.odt.co.nz/regions/queens...cause%E2%80%99
A coroner’s findings into a helicopter accident near Queenstown in 2015 has brought the safety of Robinson helicopters back into the spotlight. Longtime operators of Robinsons are pushing back, telling Public Interest Journalism Fund reporter Guy Williams the findings are speculative and the reputation of the United States company continues to be unfairly maligned.
The crash of the Robinson R44 in the Lochy River valley would not have occurred in any other type of helicopter, coroner Alexandra Cunninghame wrote in her findings last month.
The accident killed Queenstown student pilot James Patterson-Gardner (18) — who was at the controls — and experienced Wanaka pilot Stephen Combe.
The aircraft’s mid-air break-up from "mast-bumping" — when a helicopter’s main rotor hub strikes its driveshaft (mast) — has become emblematic of a widespread public perception of Robinsons as flawed helicopters prone to falling out of the sky.
With no evidence of mechanical fault or pilot error, Ms Cunninghame concluded neither caused the accident.
Despite evidence flying conditions were near perfect and winds in the area around the time of the accident were "minimal to light", she determined "on the balance of probabilities" the R44 had encountered an "abrupt change in wind direction or an abrupt gust", leading to mast-bumping and an "almost instantaneous transition from forward flight to catastrophe".
Behind her reasoning was evidence presented by an investigative engineering consultancy, Prosolve Ltd, that the Robinson rotor head design made the company’s helis "dangerously susceptible" to even light turbulence, particularly at higher speeds, and "catastrophic failure".
Alongside a call for Robinson pilots to avoid forecast moderate-to-severe turbulence, and to stay under 70 knots in mountainous terrain, the coroner called for more research into the aircraft’s design, and recommended cockpit video recorders be mandatory for all helicopters in New Zealand.
In late 2016, the Transport Accident Investigation Commission (TAIC) put Robinsons on its watchlist of "pressing concerns", citing the Lochy Valley crash as one of 14 mast-bumping accidents, in which 18 people were killed in in-flight break-ups, in the previous two decades.
The TAIC said a significant proportion of the accidents occurred in "low-G" flight conditions, a state of near-weightlessness caused by turbulence or "large or abrupt" flight control inputs.
It had concerns about the safety of Robinsons in the mountainous terrain and weather conditions common in New Zealand.
That prompted a slew of organisations to ban their staff from flying in Robinsons, including the Department of Conservation and Otago Regional Council.
The Civil Aviation Authority(CAA) responded by tightening up the training regime for Robinson R22 and R44 pilots to bring it up to international best practice.
In the past five years, the rate of Robinson accidents from any cause has fallen by two-thirds, the CAA says.
Since then, one Robinson crash has involved mast-bumping, that of Wanaka pilot Matthew Wallis at Lake Wanaka in 2018, the primary cause attributed to "severe or extreme" turbulence.
The coroner’s findings into the 2015 accident, with their implication that Robinsons are inherently dangerous, have angered longtime operators of the make.
Queenstown aviator Jules Tapper says Robinsons are safe when flown within their limits. Photo: ODT files
In an opinion piece for the Otago Daily Times last month, commercial pilot John Sarginson said they crashed more often than other makes because there were more of them operating than any other, and most pilots did their training and early flying in them.
The coroner had based her findings on evidence from one investigative engineering firm, which after finding no evidence of mechanical fault or pilot error, had speculated about the cause.
"The coroner accepted there was no evidence to show the pilots made a mistake," Mr Sarginson wrote.
"So I can only hope the coroner also accepted there was no evidence to show the pilots did not make a mistake."
Mast-bumping was a "result" in accidents, not the cause, Mr Sarginson told the ODT this week.
He had flown Robinsons for 34 years, and operated a fleet of them doing agricultural work in the southern South Island for seven years in the 2000s without a single accident.
"They’re not bulletproof, but if the pilot stays within their own limits and the aircraft’s, and knows when it’s best to be on the ground, they’re perfectly fine and well-suited to New Zealand.
"All aircraft have quirks that pilots need to be aware of, and know how to respond to."
The TAIC had put Robinsons on its watchlist "without factual cause", and it was time that stance was revisited.
However, it suited the stakeholders in aviation companies operating more powerful helicopters for Robinsons to remain on the watchlist, because they were benefiting from the work that used to be performed by Robinsons, he said.
The CAA, on the other hand, deserved a "pat on the back" for tightening up the Robinson pilot training regime, which had dramatically reduced the accident rate.
Respected Queenstown aviator Jules Tapper said he had flown in most types of aircraft over more than 60 years, and flown his own R22 for the past 27 years.
Queenstown commercial pilot John Sarginson wants Robinsons removed from a safety watchlist. Photo: supplied
"They are a light helicopter just like there are light aircraft, and they have to be flown within the parameters for which they’ve been built."
That included slowing down in turbulence and understanding the "simple" control response to a low-G situation.
Lindis Pass farmer Russell Emmerson has logged 14,000 hours in Robinsons, using them for mustering and other tasks on his vast property for the past 33 years.
The coroner’s findings were based on "pure conjecture", he said.
"We operate in extreme conditions here on many occasions, and we know their limitations.
"If we don’t have to go, we don’t go."
The "bad press" from the watchlist move and the highlighting of every Robinson accident had unfairly tarnished the helicopter maker’s reputation, Mr Emmerson said.
The Robinson company, which has sold more than 13,000 helicopters since it started production in 1979, did not take part in last year’s inquest hearings.
It has consistently maintained pilot input is the cause of crashes, and because its aircraft are flown by more student pilots and non-professional pilots.
An emailed statement from the company said the coroner’s findings were based on "opinions and a flawed analysis by an expert witness lacking expertise in helicopter rotor dynamics".
Improvements in flight training and training material in New Zealand since the 2015 crash had resulted in a significant reduction in accidents.
"Robinson continues to implement design changes to improve safety, such as cockpit video recorders as standard equipment on both R44 and R66 helicopters, and will continue its research and development into low-G flight."
Wreckage from the 2015 accident in the Lochy River valley near Queenstown. Photo: NZ Police
In her report, Ms Cunninghame reiterated the TAIC recommendation that cockpit video recorders be made mandatory in all Robinsons flying in New Zealand.
It is one thing the three veteran pilots broadly agree with her on, Mr Emmerson saying the devices would "overcome all these speculative issues".
In 2020 the CAA approved Eye in the Sky, a video, audio and flight data recorder developed by Mr Patterson-Gardner’s mother, Louisa "Choppy" Patterson, and her Queenstown-based helicopter company Over The Top.
Ministry of Transport economic regulation manager Tom Forster said it was now considering advice to the minister on the mandating of the recorders.
The CAA was also looking at non-regulatory measures to encourage greater voluntary take-up of the devices, Mr Forster said.
"Cockpit cameras not only provide valuable post-crash information to investigators, but can also be used by operators as a safety monitoring and training tool, which can provide additional safety benefits."
In the meantime, the removal of Robinsons from the watchlist appears a distant prospect.
TAIC spokesman Simon Pleasants said they were put on the watchlist out of concern at a "series of findings and recommendations" on accidents over a long time.
Taking them off the watchlist would require a "long period of that harm not happening at all".
However, progress was being made on the three actions the TAIC was seeking, Mr Pleasants said.
The Robinson company was continuing to commission research on its rotor head and driveshaft designs in zero-G flight, pilot training had improved and work was under way in government on getting cockpit video recorders into the helicopter fleet.
[email protected]
Choppers on list ‘without factual cause’
By Guy WilliamsA coroner’s findings into a helicopter accident near Queenstown in 2015 has brought the safety of Robinson helicopters back into the spotlight. Longtime operators of Robinsons are pushing back, telling Public Interest Journalism Fund reporter Guy Williams the findings are speculative and the reputation of the United States company continues to be unfairly maligned.
The crash of the Robinson R44 in the Lochy River valley would not have occurred in any other type of helicopter, coroner Alexandra Cunninghame wrote in her findings last month.
The accident killed Queenstown student pilot James Patterson-Gardner (18) — who was at the controls — and experienced Wanaka pilot Stephen Combe.
The aircraft’s mid-air break-up from "mast-bumping" — when a helicopter’s main rotor hub strikes its driveshaft (mast) — has become emblematic of a widespread public perception of Robinsons as flawed helicopters prone to falling out of the sky.
With no evidence of mechanical fault or pilot error, Ms Cunninghame concluded neither caused the accident.
Despite evidence flying conditions were near perfect and winds in the area around the time of the accident were "minimal to light", she determined "on the balance of probabilities" the R44 had encountered an "abrupt change in wind direction or an abrupt gust", leading to mast-bumping and an "almost instantaneous transition from forward flight to catastrophe".
Behind her reasoning was evidence presented by an investigative engineering consultancy, Prosolve Ltd, that the Robinson rotor head design made the company’s helis "dangerously susceptible" to even light turbulence, particularly at higher speeds, and "catastrophic failure".
Alongside a call for Robinson pilots to avoid forecast moderate-to-severe turbulence, and to stay under 70 knots in mountainous terrain, the coroner called for more research into the aircraft’s design, and recommended cockpit video recorders be mandatory for all helicopters in New Zealand.
In late 2016, the Transport Accident Investigation Commission (TAIC) put Robinsons on its watchlist of "pressing concerns", citing the Lochy Valley crash as one of 14 mast-bumping accidents, in which 18 people were killed in in-flight break-ups, in the previous two decades.
The TAIC said a significant proportion of the accidents occurred in "low-G" flight conditions, a state of near-weightlessness caused by turbulence or "large or abrupt" flight control inputs.
It had concerns about the safety of Robinsons in the mountainous terrain and weather conditions common in New Zealand.
That prompted a slew of organisations to ban their staff from flying in Robinsons, including the Department of Conservation and Otago Regional Council.
The Civil Aviation Authority(CAA) responded by tightening up the training regime for Robinson R22 and R44 pilots to bring it up to international best practice.
In the past five years, the rate of Robinson accidents from any cause has fallen by two-thirds, the CAA says.
Since then, one Robinson crash has involved mast-bumping, that of Wanaka pilot Matthew Wallis at Lake Wanaka in 2018, the primary cause attributed to "severe or extreme" turbulence.
The coroner’s findings into the 2015 accident, with their implication that Robinsons are inherently dangerous, have angered longtime operators of the make.
Queenstown aviator Jules Tapper says Robinsons are safe when flown within their limits. Photo: ODT files
In an opinion piece for the Otago Daily Times last month, commercial pilot John Sarginson said they crashed more often than other makes because there were more of them operating than any other, and most pilots did their training and early flying in them.
The coroner had based her findings on evidence from one investigative engineering firm, which after finding no evidence of mechanical fault or pilot error, had speculated about the cause.
"The coroner accepted there was no evidence to show the pilots made a mistake," Mr Sarginson wrote.
"So I can only hope the coroner also accepted there was no evidence to show the pilots did not make a mistake."
Mast-bumping was a "result" in accidents, not the cause, Mr Sarginson told the ODT this week.
He had flown Robinsons for 34 years, and operated a fleet of them doing agricultural work in the southern South Island for seven years in the 2000s without a single accident.
"They’re not bulletproof, but if the pilot stays within their own limits and the aircraft’s, and knows when it’s best to be on the ground, they’re perfectly fine and well-suited to New Zealand.
"All aircraft have quirks that pilots need to be aware of, and know how to respond to."
The TAIC had put Robinsons on its watchlist "without factual cause", and it was time that stance was revisited.
However, it suited the stakeholders in aviation companies operating more powerful helicopters for Robinsons to remain on the watchlist, because they were benefiting from the work that used to be performed by Robinsons, he said.
The CAA, on the other hand, deserved a "pat on the back" for tightening up the Robinson pilot training regime, which had dramatically reduced the accident rate.
Respected Queenstown aviator Jules Tapper said he had flown in most types of aircraft over more than 60 years, and flown his own R22 for the past 27 years.
Queenstown commercial pilot John Sarginson wants Robinsons removed from a safety watchlist. Photo: supplied
"They are a light helicopter just like there are light aircraft, and they have to be flown within the parameters for which they’ve been built."
That included slowing down in turbulence and understanding the "simple" control response to a low-G situation.
Lindis Pass farmer Russell Emmerson has logged 14,000 hours in Robinsons, using them for mustering and other tasks on his vast property for the past 33 years.
The coroner’s findings were based on "pure conjecture", he said.
"We operate in extreme conditions here on many occasions, and we know their limitations.
"If we don’t have to go, we don’t go."
The "bad press" from the watchlist move and the highlighting of every Robinson accident had unfairly tarnished the helicopter maker’s reputation, Mr Emmerson said.
The Robinson company, which has sold more than 13,000 helicopters since it started production in 1979, did not take part in last year’s inquest hearings.
It has consistently maintained pilot input is the cause of crashes, and because its aircraft are flown by more student pilots and non-professional pilots.
An emailed statement from the company said the coroner’s findings were based on "opinions and a flawed analysis by an expert witness lacking expertise in helicopter rotor dynamics".
Improvements in flight training and training material in New Zealand since the 2015 crash had resulted in a significant reduction in accidents.
"Robinson continues to implement design changes to improve safety, such as cockpit video recorders as standard equipment on both R44 and R66 helicopters, and will continue its research and development into low-G flight."
Wreckage from the 2015 accident in the Lochy River valley near Queenstown. Photo: NZ Police
In her report, Ms Cunninghame reiterated the TAIC recommendation that cockpit video recorders be made mandatory in all Robinsons flying in New Zealand.
It is one thing the three veteran pilots broadly agree with her on, Mr Emmerson saying the devices would "overcome all these speculative issues".
In 2020 the CAA approved Eye in the Sky, a video, audio and flight data recorder developed by Mr Patterson-Gardner’s mother, Louisa "Choppy" Patterson, and her Queenstown-based helicopter company Over The Top.
Ministry of Transport economic regulation manager Tom Forster said it was now considering advice to the minister on the mandating of the recorders.
The CAA was also looking at non-regulatory measures to encourage greater voluntary take-up of the devices, Mr Forster said.
"Cockpit cameras not only provide valuable post-crash information to investigators, but can also be used by operators as a safety monitoring and training tool, which can provide additional safety benefits."
In the meantime, the removal of Robinsons from the watchlist appears a distant prospect.
TAIC spokesman Simon Pleasants said they were put on the watchlist out of concern at a "series of findings and recommendations" on accidents over a long time.
Taking them off the watchlist would require a "long period of that harm not happening at all".
However, progress was being made on the three actions the TAIC was seeking, Mr Pleasants said.
The Robinson company was continuing to commission research on its rotor head and driveshaft designs in zero-G flight, pilot training had improved and work was under way in government on getting cockpit video recorders into the helicopter fleet.
[email protected]
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The right roll is often described as a snap roll and is extremely quick at around 100 degrees per second. It’s quite instinctive to try to counteract this and difficult not to make some control input to the unconventional T bar cyclic when you’ve been turned on your side at that rate without warning. I’ve spoken to people who’ve had it demonstrated to them numerous times when it used to be in the training syllabus (late 80’s early 90’s). One of the most respected UK Robinson instructors left to demonstrate low G with a student and sadly had a fatal accident (the training notes said as much and this was detailed in the investigation). Later Robinson decided it wasn’t safe to demonstrate and removed it from the training syllabus.
ON 7/27/83, MILD MAST BUMPING OCCURRED DURING A PUSHOVER MANEUVER WHILE A HILLER FH-1180 WAS ON A FLT TO CERTIFY NEW ROTOR BLADES. PRIOR TO THE INCIDENT, THE HELICOPTER WAS ACCELERATED TO 90 MPH. THIS WAS FOLLOWED BY A PULL-UP & DECELERATION TO 80 MPH, THEN THE PUSHOVER WAS INITIATED. THE HELICOPTER REPORTEDLY ROLLED SHARPLY TO THE RIGHT & PITCHED NOSE DOWN WITH SOME YAW TO THE RIGHT. RECOVERY WAS MADE WITH LEFT CYCLIC; HOWEVER, DIRECTIONAL CONTROL WAS LOST BEFORE RECOVERY & MILD MAST BUMPING. ON 7/28/83, FH-1100, N450FH, A STANDARD PRODUCTION MODEL, WAS FLOWN TO EXPLORE THE PHENOMENON. AFTER 2 PUSHOVERS WITH INCREASING SEVERITY, IN WHICH CONTROL WAS RETAINED, THE PLT ATTEMPTED A REPETITION OF THE PREVIOUS DAY'S MANEUVER. WITNESSES OBSERVERVED THE HELICOPTER ROLL & YAW TO THE RIGHT & PITCH DOWN AS IT BEGAN TO BREAK UP, THEN BURN & CRASH. AN EXAM REVEALED THE MAIN ROTOR BLADES SEPARATED AFTER MAST BUMPING & MAST FAILURE OCCURRED. THERE WAS EVIDENCE THE PLT MIGHT NOT HAVE BEEN CURRENT IN TEETERING ROTOR SYSTEMS & RECOVERY FROM LOW G ROLLS.
Afraid I can't see rotor separation, am I missing something? Certainly quick.
https://www.youtube.com/watch?v=7P3zYDgnYew&t=28s
https://www.youtube.com/watch?v=7P3zYDgnYew&t=28s
What also struck me was the speed at which this unfolded. That was barely more than 1s between initiation and an unrecoverable situation. Don't try this at home...
If the pilot does absolutely nothing with the cyclic upon encountering a right roll in low-g, will the mast still bump?
The TR is causing the roll so 'theoretically' right pedal might help but it's not something I would try.
There is only one answer - fly the aircraft within its limits and avoid low g at all costs.
