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General Aviation Safety
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: Issue an airworthiness directive mandating compliance with Cessna Service Bulletin 550-24-14, "Control Wheel Electrical Cable Replacement," which was issued on January 17, 1992.
Original recommendation transmittal letter:
Closed - Unacceptable Action
Milwaukee, WI, United States
Loss of Control and Impact with Water, Marlin Air Cessna Citation 550, N550BP
Addressee(s) and Addressee Status:
FAA (Closed - Unacceptable Action)
Safety Recommendation History
The FAA and Cessna conducted a design review of the control column wiring, a system safety assessment to examine the likelihood of a pitch trim runaway, and a service history review. The service history review also examined the service history of other Cessna models with similar control column wiring designs. All of these reviews and analyses examined whether wire shorting in the control column could lead to an unarrestable pitch trim runaway. Cessna and the FAA believe that an uncommanded, unarrestable pitch trim runaway caused by control column wiring faults is extremely improbable. In the letter that transmitted this recommendation to the FAA, we pointed out that Cessna had received numerous customer reports of short circuits and cut wires after the issuance of the SB. In its current letter, the FAA stated that the review of service difficulty reports, which it had conducted in conjunction with Cessna, did not reveal any significant issues with the control column wiring installation, and that it had not found instances of electrical arcing or wire-to-wire shorts that would have caused an uncommanded, unarrestable pitch trim runaway. The FAA concluded that the issuance of an AD is not warranted and considers its actions in response to this recommendation to be complete. The NTSB’s investigation of the June 4, 2007, Milwaukee accident revealed that, after issuance of the SB, Cessna received seven reports about wiring failures in the control column. Below is information taken from the Airworthiness Factual Report on the Milwaukee accident, dated March 26, 2008: Since issuance of the Service Bulletin, Cessna records show the following seven further reports about wiring failures in the control column. Unique ownership and serial identifiers have been omitted. This information came from the CSINFO database with the following parameters: Issue IDs: 31393, 51365, 7876, 327636, 131348, 214650, and 9461427. 1. Model: CIII – 650 Date: 11/16/2007 Description: Autopilot will not initialize, unable to engage system. Solution: Found ribbon cable shorted to the airframe in the control column. Replaced control column ribbon cable. 2. Model: CIII – 650 Date: 01/23/2004 Description: Horizontal stab trim is pulsing in one direction uncommanded. Solution: Repaired wiring in the control column. 3. Model/Serial: CJ-525 Date: 04/03/2003 Description: The autopilot will not engage. Solution: Repaired wiring in pilot's control yoke. 4. Model/Serial: CJ-560 Date: 06/30/1999 Description: 7.5 ampere autopilot circuit breaker disengaged when activating the pilot's TCS switch. Solution: Wire shorted in pilot’s control column. 5. Model/Serial: Excel 560 Date: 11/29/2005 Description: Pilot’s Touch Control Steering inoperative. Cause: Wires pinched by control yoke cross bolts. Solution: Replaced pinched wires in the control column. 6. Model/Serial: SII – S550 Date: 08/27/2001 Description: SCR 211212 Service bulletin requested for change of ribbon cable in both control yokes with new style cable. Solution: Service bulletin SBS550-24-12, Control Wheel Electrical Cable Replacement, has been released since 1992. 7. Model/Serial: CJ-550 Date: 12/19/2000 Description: Ribbon wire cut in the left control column. Solution: Order parts listed in SBS550-24-12. Although the FAA and Cessna may not believe these seven cases to be significant, the NTSB believes that a short circuit in the control column wiring has the potential to result in a pitch trim runaway. If a problem were reported seven times after Cessna issued the SB, the SB clearly did not adequately address the problem. However, because the FAA does not believe the recommended action is needed and does not plan further action, Safety Recommendation A-09-116 is classified CLOSED—UNACCEPTABLE ACTION.
- From J. Randolph Babbitt, Administrator: We conducted a design review of the control column wiring, a system safety assessment to examine the likelihood of a pitch trim runaway, and a service history review. Other Cessna models contain similar control column wiring designs, so we expanded the scope of the review to include these other Cessna models. The following table shows the models that share the same or similar ribbon cable design in the control yokes. (Note; this is the total population originally built wilh ribbon cable): Model Service Bulletin (SB) Date Serial Number (S/N) Compliance SB S/N 500/501 SB500-24-16R1 Mar 13/92 0001-0689 Optional 689 550/551 SB550-24-14R1 Mar 13/92 0002-0629 Optional 628 S550 SB550-24-12R2 Mar 13/92 0001-0160 Optional 160 552 None N/A N/A N/A 0 560 SB560-24-01R1 Mar 13/92 0001-0051 Optional 51 650 SB650-24-44 Sept 1/92 0001-0216 Optional 216 Total S/N 1744 We requested Cessna perform an analysis to determine if cross-coupling (shorting) of wires in the control column could lead to an unarrestable pitch trim runaway. The analysis revealed that "uncommanded, unarrcstable pitch trim runaway due to control column wiring faults" is extremely improbable. Additionally, the analysis included another failure condition titled "uncommanded autopilot servo motion due to control column wiring faults." which was also shown qualitatively to be extremely improbable. We reviewed and concurred with this analysis. We also examined details regarding procedures to detect wire failures and faults in the control yoke through the preflight inspection outlined in the aircraft night manual (AFM) and maintenance checks. We found these checks to be clear and sufficient to detect potential control yoke wiring failures, thus minimizing the potential exposure to any latent failures, and verifying system function prior to every flight. In its November 17, 20 I0, letter the Board indicated that Cessna received numerous customer reports of short circuits and cut wires after the issuance of the Service Bulletin. The FAA and Cessna review of service difficulty report information has not revealed any significant issues with the control column wiring installation, and did not find instances of electrical arcing or wire-to-wire shorts that would have caused an uncommanded, unarrestable pitch trim runaway. We have concluded that the issuance of an FAA airworthiness directive is not warranted. I believe the FAA has effectively addressed this safety recommendation, and I consider our actions complete.
The FAA's planned response of examining the service history following the issuance of the service bulletin is a necessary step in the process of developing an AD. The letter that transmitted this recommendation to the FAA indicated that, after SB 550-24-14 had been issued, Cessna received numerous customer reports of short circuits and cut wires in control columns in various Citation models. In each case for which sufficient data were available, analysis indicated that the actions suggested in SB 550-24-14 would likely have alleviated the situation. Accordingly, pending issuance of the recommended AD, Safety Recommendation A-09-116 is classified OPEN – ACCEPTABLE RESPONSE.
Letter Mail Controlled 5/5/2010 12:17:19 PM MC# 2100167 - J. Randolph Babbitt, Administrator: We will examine the service history following the issuance of Cessna Service Bulletin 550-24-14 prior to making a determination of mandatory action and report our findings in our follow-on response. I will provide an update on the progress of this safety recommendation by March 2011.
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