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On January 4, 2009, about 1409 central standard time, a dual-engine Sikorsky S-76C++ helicopter, N748P, registered to and operated by PHI, Inc., departed controlled flight and crashed into marshy terrain about 7 minutes after takeoff. Both pilots and six passengers on board were fatally injured, and one passenger was seriously injured. The helicopter was substantially damaged. The helicopter departed Lake Palourde Base Heliport in Amelia, Louisiana, en route to the South Timbalier oil platform in the Gulf of Mexico. No flight plan was filed with the Federal Aviation Administration (FAA)1 for the 14 Code of Federal Regulations (CFR) Part 135 air taxi flight, nor was one required.
TO THE FEDERAL AVIATION ADMINISTRATION: Require Sikorsky to design an audible low rotor revolutions per minute (Nr) alarm system and master warning light that will alert the flight crew of S-76 model helicopters of rapidly decaying Nr.
Original recommendation transmittal letter:
Closed - Unacceptable Action
Morgan City, LA, United States
Addressee(s) and Addressee Status:
FAA (Closed - Unacceptable Action)
Safety Recommendation History
The National Transportation Safety Board (NTSB) has reviewed the Federal Aviation Administration’s (FAA) notice of proposed rulemaking (NPRM) titled, “Normal and Transport Category Rotorcraft Certification,” which was published at 82 Federal Register 50583 on November 1, 2017. The NPRM proposes to amend the certification standards of normal- and transport category helicopters. The proposed changes would reduce or eliminate the need for certain special conditions currently required to obtain certification of modern rotorcraft and would also incorporate the requirements of equivalent level of safety findings that the FAA has imposed as conditions for approving certain design features. The FAA is proposing the changes to address modern designs currently used in the rotorcraft industry and to reduce the burden on applicants for certification of new rotorcraft designs. We have reviewed the NPRM and provide comments below regarding specific sections of this NPRM. Sections 27.1309 and 29.1309, “Equipment, systems, and installations.” The NPRM proposes revisions to sections 27.1309 and 29.1309, which indicate design and installation criteria for equipment, systems, and installations to ensure that they perform their intended functions under any foreseeable operating condition. Regarding proposed subsection (c), which discusses a means to alert the crew in the event of a failure, we suggest including language to indicate that the alert should occur in a timely manner. In addition, we suggest adding language to indicate that an appropriate alert, including assessment of the need for multiple sensory modality warnings, must be provided if immediate pilot awareness and immediate or subsequent corrective action is required. We note that we have previously issued recommendations to the FAA regarding the need for multiple sensory modality warnings (visual and aural) in both airplanes and helicopters. (For more information, see Safety Recommendations A-07-35, A-07-52, A-09-117, A-10-142, and A-10-143, which can be accessed from the Safety Recommendations page on our website (www.ntsb.gov).) For example, after a January 4, 2009, accident involving a dual-engine Sikorsky S-76C++ helicopter that departed controlled flight and crashed about 7 minutes after takeoff from Lake Palourde Base Heliport, Amelia, Louisiana, we issued Safety Recommendation A-10-144, which asked the FAA to do the following: Revise [Title] 14 Code of Federal Regulations 27.33 and 29.33 to require an audible low rotor revolutions per minute alarm system and master warning light for all dual engine helicopters, even those that are equipped with a device that automatically increases power on the operating engine when the other engine fails. On February 16, 2017, we classified this recommendation “Closed—Unacceptable Action” after the FAA indicated (in 2015) that it was anticipating restructuring airworthiness standards but did not take timely action to address this recommendation. Although this recommendation is closed, we believe the subject is still relevant, and, in its review of sections 27.1309 and 29.1309, the FAA should consider requiring applicants to address alerting through multiple sensory modalities (visual and aural or visual and tactile) to help ensure the timely capture and direction of a pilot’s attention to the condition triggering the alert.
We continue to believe that an audible low Nr alarm system and master warning light would help to alert pilots of all dual-engine helicopters of a decaying Nr condition, including those equipped with a device that increases power on the operating engine when the other engine fails. However, because the FAA has indicated that its actions in response to these recommendations are complete and it will take no further action, Safety Recommendations A-10-142 and -143 are classified CLOSED—UNACCEPTABLE ACTION.
-From Tony Fazio, Director, Office of Accident Investigation and Prevention: The Board's response refers to other products that exceed the requirements of section 29.33 (amendment 29-15). The information provided by the Board illustrates how some helicopter models exceeded the certification requirements by providing low rotor RPM warning even though there were other safeguards in place. The Board also points out that the FAA issued a notice of proposed rulemaking to incorporate redundant sensory cuing. The S-76 incorporated the requirements of section 29.33 (amendment 29-3). Our regulations contain the regulatory standard that must be met for certification. We allow, but do not mandate, applicants to exceed the requirements of our regulations. If we determine that an unsafe condition exists, we may mandate a redesign to mitigate the unsafe condition; and the applicant may propose to meet a later certification basis as the mitigation However, as stated in our initial response, there is not a record indicating an unsafe condition exists. With the exception of this single accident, our data shows no similar accidents or incidents. The Board asked the FAA to reconsider its actions related to Safely Recommendations A-10-138, -142, and -143, in its July 11, 2011 letter. We carefully reconsidered our actions, and we continue to find that our response to these safety recommendations reflect the best interests of aviation safety. Accordingly, we will take no further action in direct response to these safety recommendations, or to Safety Recommendation A-10-137.
The FAA indicated that failure or malfunction of any engine or system that would affect any engine would not prevent continued safe operation of the remaining engine. In addition, the FAA stated that the improved throttle provides the level of redundancy and isolation of systems that would allow the pilot to maintain safe rotor speed, alleviating the need for the recommended action. However, the NTSB remains concerned that a low Nr condition could result from uncommanded throttle movement of both engines simultaneously, as was the case in the 2009 PHI accident; in such case, no working engine would be available to increase power. The NTSB points out that most single- and dual-engine helicopter models are equipped with an audible alarm and/or warning light to alert the flight crew of a low Nr condition. Bell Helicopter dual-engine models 212, 412, and 430 are equipped with an audible alarm and warning light to notify the flight crew if the Nr starts decaying and falls below the specified threshold. Both the Sikorsky S-92A and the S-76D (which is currently undergoing certification) have an audible low Nr warning system, even though those helicopters are equipped with a device that automatically increases power on the operating engine. In addition, the FAA issued a notice of proposed rulemaking (NPRM), titled “Flightcrew Alerting,” that proposed to incorporate redundant sensory cuing into alerts for conditions requiring immediate flight crew awareness. The NTSB continues to believe that an audible low Nr alarm system and master warning light would help to alert pilots of all dual-engine helicopters, including those equipped with a device that increases power on the operating engine when the other engine fails, of a decaying Nr condition, and we therefore urge the FAA to reconsider its position. Pending our review of a plan to address these recommendations, Safety Recommendations A-10-142 and -143 are classified OPEN—UNACCEPTABLE RESPONSE.
CC# 201100057: - From J. Randolph Babbitt, Administrator: The S-76 is a dual-engine helicopter designed to the Category A engine isolation requirements of § 29.903, which specify that a failure or malfunction of any engine, or the failure of any system that can affect any engine, will not prevent continued safe operation of the remaining engine or require immediate action by any crewmember for continued safe flight. Additionally, searches in multiple accident databases for S-76 dual engine failures over the last 20 years resulted in no such instances, except for the accident related to this safety recommendation. Our findings demonstrate that the S-76 with the improved throttle provides the level of redundancy and isolation of systems that would allow the pilot to maintain a safe rotor speed thus alleviating the need for a low Nr audible and visual warning system. I believe we have satisfactorily responded to this recommendation, and I consider our actions complete.
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