RVDT
22nd Aug 2008, 00:26
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.