NOTAR AD Extended
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NOTAR AD Extended
DATE: August 20, 2008
AD #: 2008-18-51
This Emergency Airworthiness Directive (AD) is prompted by reports that two Model MD900 helicopters experienced broken Vertical Stabilizer Control System (VSCS) adapter tubes. In one case, the helicopter experienced uncommanded yaw, resulting in loss of a window and a door.
The same part-numbered adapter tube is used on the Model 500N and 600N helicopters Yaw Stability Augmentation System (YSAS). Some of the VSCS and YSAS adapter tubes were not manufactured to the required specifications and can fail. This condition, if not corrected, could result in loss of yaw control and subsequent loss of control of the helicopter. We have reviewed MDHI Service Bulletins SB500N-040 for the Model 500N helicopters andSB600N-047 for the Model 600N helicopters, dated August 15, 2008, with YSAS adapter tubes installed. We have also reviewed Service Bulletin SB900-109, dated August 15, 2008, for the Model MD900 helicopters with VSCS adapter tubes installed. These service bulletins specify de-energizing
the YSAS or the VSCS and installing a placard that limits the airspeed. The service bulletins specify removing the placard when the YSAS and VSCS adapter tubes are replaced with airworthy parts. The manufacturer anticipates having airworthy YSAS and VSCS adapter tubes available within the next 30 to 60 days. The FAA anticipates requiring that the YSAS and VSCS adapter tubes be replaced with the airworthy parts as a terminating action to the requirements of this AD.
This unsafe condition is likely to exist or develop on other helicopters of these same type designs. Therefore, this AD requires the following before further flight:
For Model 500N and 600N helicopters:
• De-energize the YSAS, pull the circuit breaker, and install a plastic cable tie on the circuit breaker to prevent accidental operation of the YSAS.
• Install a placard on the instrument panel as close as practicable to the airspeed indicator that states:
“YSAS SYSTEM DE-ENERGIZED. AIRPSEED LIMIT 100 KIAS or VNE, WHICHEVER IS LESS.”
For Model MD900 helicopters:
• De-energize the VSCS.
• Disable the Autopilot/VSCS (AP/SAS) and install a placard stating that the AP/SAS is deactivated.
• Install a placard on the instrument panel as close as practicable to the airspeed indicator that states:
“VSCS SYSTEM DE-ENERGIZED. AIRPSEED LIMIT 100 KIAS or VNE, WHICHEVER IS LESS.”
• Make pen and ink changes or place a copy of this AD in the airworthiness limitations section of the RFM to revise the airworthiness limitations as follows:
• VNE is limited to 100 KIAS or less as determined by referring to the airspeed VNE placard already installed on the helicopter.
• Use of the autopilot is prohibited.
For the Model MD900 helicopters, do the actions by following the specified portions of the service bulletin described previously.
This rule is issued under 49 U.S.C. Section 44701 pursuant to the authority delegated to me by the Administrator, and is effective immediately upon receipt of this emergency AD.
AD #: 2008-18-51
This Emergency Airworthiness Directive (AD) is prompted by reports that two Model MD900 helicopters experienced broken Vertical Stabilizer Control System (VSCS) adapter tubes. In one case, the helicopter experienced uncommanded yaw, resulting in loss of a window and a door.
The same part-numbered adapter tube is used on the Model 500N and 600N helicopters Yaw Stability Augmentation System (YSAS). Some of the VSCS and YSAS adapter tubes were not manufactured to the required specifications and can fail. This condition, if not corrected, could result in loss of yaw control and subsequent loss of control of the helicopter. We have reviewed MDHI Service Bulletins SB500N-040 for the Model 500N helicopters andSB600N-047 for the Model 600N helicopters, dated August 15, 2008, with YSAS adapter tubes installed. We have also reviewed Service Bulletin SB900-109, dated August 15, 2008, for the Model MD900 helicopters with VSCS adapter tubes installed. These service bulletins specify de-energizing
the YSAS or the VSCS and installing a placard that limits the airspeed. The service bulletins specify removing the placard when the YSAS and VSCS adapter tubes are replaced with airworthy parts. The manufacturer anticipates having airworthy YSAS and VSCS adapter tubes available within the next 30 to 60 days. The FAA anticipates requiring that the YSAS and VSCS adapter tubes be replaced with the airworthy parts as a terminating action to the requirements of this AD.
This unsafe condition is likely to exist or develop on other helicopters of these same type designs. Therefore, this AD requires the following before further flight:
For Model 500N and 600N helicopters:
• De-energize the YSAS, pull the circuit breaker, and install a plastic cable tie on the circuit breaker to prevent accidental operation of the YSAS.
• Install a placard on the instrument panel as close as practicable to the airspeed indicator that states:
“YSAS SYSTEM DE-ENERGIZED. AIRPSEED LIMIT 100 KIAS or VNE, WHICHEVER IS LESS.”
For Model MD900 helicopters:
• De-energize the VSCS.
• Disable the Autopilot/VSCS (AP/SAS) and install a placard stating that the AP/SAS is deactivated.
• Install a placard on the instrument panel as close as practicable to the airspeed indicator that states:
“VSCS SYSTEM DE-ENERGIZED. AIRPSEED LIMIT 100 KIAS or VNE, WHICHEVER IS LESS.”
• Make pen and ink changes or place a copy of this AD in the airworthiness limitations section of the RFM to revise the airworthiness limitations as follows:
• VNE is limited to 100 KIAS or less as determined by referring to the airspeed VNE placard already installed on the helicopter.
• Use of the autopilot is prohibited.
For the Model MD900 helicopters, do the actions by following the specified portions of the service bulletin described previously.
This rule is issued under 49 U.S.C. Section 44701 pursuant to the authority delegated to me by the Administrator, and is effective immediately upon receipt of this emergency AD.
Thread Starter
FNW,
What ho squiffy!
Sorry about that chap! The comment was for the non members of the Old Boy network who do not have passing interest in the banter about the cabbage crates over on the "G-WOPPAS" thread.
May be the "mod" should change the title of that thread as it seems to be a subject of some concern to the community (fraternity?) and may be important as it is an Emergency Airworthiness Directive.
Toodle pip!
What ho squiffy!
Sorry about that chap! The comment was for the non members of the Old Boy network who do not have passing interest in the banter about the cabbage crates over on the "G-WOPPAS" thread.
May be the "mod" should change the title of that thread as it seems to be a subject of some concern to the community (fraternity?) and may be important as it is an Emergency Airworthiness Directive.
Toodle pip!
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I see that MDH have revised SB900-109, which relates to the MD902.
It no longer requires that the VSCS circuit breakers be pulled and allows the system to be switched back on in the event of a NOTAR problem.
This sounds sensible. I wonder if the Emergency AD will be revised as well?
It no longer requires that the VSCS circuit breakers be pulled and allows the system to be switched back on in the event of a NOTAR problem.
This sounds sensible. I wonder if the Emergency AD will be revised as well?
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There is an AMOC that was issued the same day as Rev1 to SB900-109. Alternate Method of Compliance. I would expect to see a rev to the AD when the FAA goes back to the first of the week.
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Does this mean that the suspect control rods are exempt from failure if the VSCS system is turned back on due to a NOTAR emergency?
And at what exact point of the final approach with a NOTAR emergency are you supposed to select the VSCS off?
And at what exact point of the final approach with a NOTAR emergency are you supposed to select the VSCS off?
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Does this mean that the suspect control rods are exempt from failure if the VSCS system is turned back on due to a NOTAR emergency?
If you want 100% safety, don't go flying, or cross the road, or get out of bed!
And at what exact point of the final approach with a NOTAR emergency are you supposed to select the VSCS off?
Any comments from other MD900/902 pilots would be welcome.
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Reference the above and to clarify matters:-
For those who are not aware of SB900-109R1, it now says:
For those who are not aware of SB900-109R1, it now says:
Keep VSCS de−energized unless helicopter is experiencing a anti−torque system malfunction.
If there is a anti−torque system malfunction, de−energize the VSCS on final approach to a run on landing.....
If there is a anti−torque system malfunction, de−energize the VSCS on final approach to a run on landing.....
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No, but I don't think that practicing for a failure of both systems at the same time has ever been considered prior to the last two weeks.
I have flown with the VSCS switched off though. There is certainly a yaw stability problem at high speeds but not at the lower speeds of a final approach where the VSCS loses its authority anyway.
My previous comments were a discusion about SB900-109R1. Forget the AD for the moment because that certainly complicates matters. I would not want to be flying anyway if I was subject to its requirements.
Lets put ourselves in a hypothetical situation where we are subject to SB900-109R1 only. We are flying along below 100 knots with the VSCS switched off. The revised SB no longer requires that the circuit breakers be pulled, so they are available to us. We suddenly diagnose a NOTAR problem.
We immediately switch the VSCS back on and pray that we don't then get an adapter tube failure. I think the chances would be fairly remote. We then carry out the standard actions for a 'Yaw Control Failure'. The SB then says:
Now, I don't know why you would want to switch the VSCS back off at this point but that's what the SB says. Personally, I would leave them on rather than complicate the situation, particularly in a 'Right Pedal Forward' situation. I might consider it in a 'Left Pedal Forward' situation if everything else was going to plan, but why bother. As I said before, the VSCS have minimal authority at the lower speeds and I suspect that an adapter tube failure at that point would have little consequence anyway.
But, anonythemouse, referring to the SB, asked the question "at what exact point of the final approach with a NOTAR emergency are you supposed to select the VSCS off?" You saw my comments, would you not agree?
I have flown with the VSCS switched off though. There is certainly a yaw stability problem at high speeds but not at the lower speeds of a final approach where the VSCS loses its authority anyway.
My previous comments were a discusion about SB900-109R1. Forget the AD for the moment because that certainly complicates matters. I would not want to be flying anyway if I was subject to its requirements.
Lets put ourselves in a hypothetical situation where we are subject to SB900-109R1 only. We are flying along below 100 knots with the VSCS switched off. The revised SB no longer requires that the circuit breakers be pulled, so they are available to us. We suddenly diagnose a NOTAR problem.
Keep VSCS de−energized unless helicopter is experiencing a anti−torque system malfunction.
If there is a anti−torque system malfunction, de−energize the VSCS on final approach to a run on landing......
But, anonythemouse, referring to the SB, asked the question "at what exact point of the final approach with a NOTAR emergency are you supposed to select the VSCS off?" You saw my comments, would you not agree?
