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On June 4, 2007, about 1600 central daylight time, a Cessna Citation 550, N550BP, impacted Lake Michigan shortly after departure from General Mitchell International Airport, Milwaukee, Wisconsin (MKE).1 The two pilots and four passengers were killed, and the airplane was destroyed. The airplane was being operated by Marlin Air under the provisions of 14 Code of Federal Regulations (CFR) Part 135 and departed MKE about 1557 with an intended destination of Willow Run Airport (YIP), near Ypsilanti, Michigan. At the time of the accident flight, marginal visual meteorological conditions prevailed at the surface, and instrument meteorological conditions prevailed aloft; the flight operated on an instrument flight rules flight plan.
TO THE FEDERAL AVIATION ADMINISTRATION: Require Cessna to modify all Citation series airplanes by incorporating an aural pitch trim-in-motion warning and contrasting color bands on the pitch trim wheel to help pilots recognize a runaway pitch trim condition before control forces become unmanageable. (A-09-117) (This recommendation supersedes Safety Recommendation A-07-52)
Original recommendation transmittal letter:
Closed - Reconsidered
Milwaukee, WI, United States
Loss of Control and Impact with Water, Marlin Air Cessna Citation 550, N550BP
Addressee(s) and Addressee Status:
FAA (Closed - Reconsidered)
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.
Thank you for the description of the extensive evaluation of this recommendation conducted by the FAA and Cessna, including the flight test of a Cessna 550 in June 2010, which determined that the Cessna 550 trim system complies with the certification standards in Part 25, both at the time the airplane was certified and currently. We acknowledge the finding from this flight test that the pitch trim wheel was visually blocked by the pilot’s knee and, as a result, the FAA’s belief that the recommended incorporation of contrasting color bands on the manual pitch trim wheel would not improve the pilot’s situational awareness. We also acknowledge the finding that, during the course of a normal flight, the pitch trim frequently changes. As a result, an aural pitch trim-in-motion warning also would not improve situational awareness. As part of its investigation, the FAA searched the NTSB’s accident/incident data base for pitch trim events involving Cessna Citation series aircraft. The FAA was only able to identify the event in Penn Cove, Washington, which had been the basis for our issuing Safety Recommendation A-07-52, which was later superseded by Safety Recommendation A-09-117. In the letter that transmitted this recommendation to the FAA, the NTSB stated, “The NTSB’s accident/incident database contains at least eight accidents involving Cessna Citation pitch trim or related failures.” The FAA requested that we provide a list of these eight accidents/incidents; we have subsequently determined that, although at least eight accidents were identified in which pitch trim, or failures to control the horizontal stabilizer or autopilot pitch were involved, the accidents/incidents involved several models of airplanes. Other than the Penn Cove, Washington, accident and the accident in Milwaukee that prompted us to issue Safety Recommendation A-09-117, we did not find any other Cessna Citation events involving pitch trim or related failures. We apologize for this error in our safety recommendation issuance letter. The NTSB disagrees with the FAA that a pilot receives enough other cues of a pitch trim runaway, in enough time to take appropriate action, while control force inputs remain within a reasonable range. However, we acknowledge the findings of the FAA, discussed above, that the recommended aural warning and markings on the pitch trim wheel are not likely to be effective in addressing our concern. As a result, Safety Recommendation A-09-117 is classified CLOSED—RECONSIDERED.
- From J. Randolph Babbitt, Administrator: We have completed our investigation into this recommendation and we do not concur that an aural trim-ill-motion and a pitch trim wheel with contrasting color bands be incorporated on any orthe Cessna Citation series airplanes. The Cessna 550 is not unique in that it does not have a trim-ill-motion system. In fact, many airplanes only incorporate a trim-in-motion system to facilitate the utilization of a faster pitch trim speed, not as a means of improving situational awareness. By providing a trim-in-motion indication, the malfunction time utilized during certification testing can be shortened, as the trim-in-motion system provides immediate recognition of pitch trim movement. We conducted a review of the data associated with the type certification testing conducted on the Cessna 550 trim system and found it to be in compliance with the part 25 standards specified in its certification basis. These standards are still valid for use on similar systems under the current part 25 requirements. Because this airplane docs not incorporate a trim-in-motion system, critical pitch trim runaways were evaluated by inducing a runaway for a time period of pilot recognition plus three seconds. After this the pilot activated the autopilot trim/disengage switch and initiated recovery of the aircraft. These tests were conducted in the most adverse loading and night conditions for the aircraft In all cases the aircraft was shown to comply with the applicable part 25 requirements including staying in a 0 to 2 g acceleration envelope within the elevator force requirements of § 25.143. Data was collected during a June 14,2010, night test evaluation by Cessna and the FAA on Cessna 550. S/ 550-0252. These night tests provided data that showed that elevator mistrim forces with full nose down trim would have been controllable if the airspeed had been managed. For airspeeds below approximately 220 knots indicated airspeed, elevator forces with full nose down trim were below the short terml1laximum control force limits in § 25.143(d). This is consistent with the observation that the accident airplane was controllable without much exertion when the airplane was operating at a relatively slow airspeed shortly after takeoff but the pilot increasingly struggled as the airplane accelerated due to increasing control forces. Recommendation A-09-114 implies that the pilot could have unintentionally engaged the autopilot in lieu of the yaw damper. If the pilot did not recognize that the autopilot was engaged and continued to pull back on the control column, the pitch trim would nm in the nose down direction until it hit the full nose down trim limit. A scenario such as this is not required to be tested during certification, as it is clear that the pilot is in the loop and cognizant of the increasing forces. Therefore, it would be expected that the pilot would take immediate action to alleviate the forces. We believe sufficient indications exist for an appropriately type-rated flightcrew to recognize an inadvertent engagement of the autopilot. The operation of the Cessna 550 and all other Cessna Citation model aircraft require a pilot type rating. Therefore, flightcrews are trained in the use of the autopilot/trim disconnect switch to address trim-related problems. As part of our investigation we conducted a search of the Board's accident history for this aircraft and other Cessna Citation models to identify possible pitch trim events. We evaluated the last 10 years of data, performing multiple searches. Our searches indentified only one accident, SEA03 FA 147, that involved loss of pitch trim control. The Cessna Citation model involved in this accident was addressed by Airworthiness Directive 2004•14-20. Based on our review, the accident history does not support a modification to this aircraft or others with similar trim system designs within the Cessna Citation fleet. In the Board's November 11, 2010 letter they state they had identified at least eight Cessna Citation accidents in the Board's database that involve pitch trim or related failures. As our review of the Board's data significantly differs, we ask the Board to provide a listing of these events for our review. We evaluated the Board's recommendation of color bands on the pitch trim wheel as a means of improving situational awareness 10 a pitch trim malfunction. During a flight evaluation by Cessna and the FAA on June 14, 2010 on Cessna 550, S/N 550•0252, the pitch trim wheel was visually blocked by the pilot's knee, but pitch trim wheel movement could be felt by the pilot’s leg. It was the judgment of the flightcrew that with the pitch trim wheel out of the field of view, incorporation of contrasting color bands on the manual pitch trim wheel would not improve situational awareness. During the course of a night, the pitch trim is frequently moving. With the motion expected, additional annunciation would not necessarily improve situational awareness. There are other acceptable cues of trim motion that allow a pilot to recognize undesired trim motion. such as unexpected or uncommanded deviation in flight path. Additionally, electric trim operation including evaluation of the disconnect switch is checked before every night, thus assuring its function. In the event of a pitch trim runaway. The pilot has the ability to manually trim out the pitch forces after disconnecting the electric trim. Also, contrasting color bands would be of little value in the recognition of uncommanded pitch trim motion, as the trim wheel is not in the primary or normal field of view. I believe the FAA has effectively addressed this safety recommendation, and I consider our actions complete.
This recommendation superseded Safety Recommendation A-07-52. To date, the FAA has not taken action to address either Safety Recommendation A-09-117 or A-07-52. In the letter that transmitted this recommendation to the FAA, the NTSB stated that our accident/incident database contained at least eight accidents involving Cessna Citation pitch trim or related failures. The FAA's April 28, 2010, letter stated that Cessna had informed the FAA that the airplane in the Marlin Air accident had not appeared to suffer a pitch trim runaway, a position based on "the fact that pitch trim was found to be in a neutral or slightly nose down position." This statement by Cessna is at odds with the NTSB's findings. The paragraph below is taken from Section 184.108.40.206 "Airplane Trim Systems" of the NTSB report on this accident: Examination of the recovered pitch trim system components revealed that the cockpit pitch trim indicator was found at the forward end of the range of travel, indicating a full nose down position, with corresponding scratches on the side of the adjacent pedestal structure. The trim tab on the right elevator was twisted and bent but generally oriented in an airplane nose-down position. Pitch trim jackscrew measurements also indicated that the pitch trim was at or near its full nose-down position [emphasis added]. Accordingly, pending the FAA's reconsideration and completion of the recommended action, Safety Recommendation A-09-117 remains classified OPEN – UNACCEPTABLE RESPONSE.
Letter Mail Controlled 5/5/2010 12:17:19 PM MC# 2100167 - From J. Randolph Babbitt, Administrator: As part of our effort to address the Board's concerns regarding trim in motion, we are working with Cessna to understand the autopilot's ability to mask the pilot's recognition of a pitch trim runaway. Further, we are examining flight test data from the model 525 to verify that it was adequately tested during certification. Based on our findings, if we deem necessary, flight test evaluations will be performed to examine the pitch trim indications and the pilot's ability to recognize and react to a pitch trim runaway. It should be noted that the pitch trim indication design is not unique to Citation series airplanes. Therefore, we are examining the service history associated with these types of designs to look for any indication of a deficiency. Additionally, specific to the Cessna 550 accident identified in this Safety Recommendation, the FAA's Wichita Aircraft Certification Office (ACO) received feedback from Cessna that indicates this airplane did not appear to suffer a pitch trim runaway. This is based on the fact that pitch trim was found to be in a neutral or slightly nose down position. I will provide an update on the progress of this safety recommendation by March 2011.
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