Evidence of Possible Malfunctions (Reply given to Lord Brennan—Minutes of Evidence, Q584)

  We must remember Undemanded Flying Control Movements (UFCM) caused by hydraulic contamination. I should therefore have added that apart from the fault E5 code found in the wreckage, another positive residual clue of a possible malfunction was found, as mentioned in the Macdonald report (5.2 and Appendix D). Metal particles found in a hydraulic system were similar to contamination found on a CH47D US Army Chinook after it rolled of its own accord onto its back, then completed the roll through 360º to a wheels down attitude at 250 feet, narrowly avoiding a crash in 1997. The Recommendations from Report USASC 97-305, following the investigation of this incident, may be found on page 3 of Attachment 1. The attachment is the same as Appendix A of the Macdonald Report Draft Addendum 3, circulated to the Select Committee immediately before the inquiry on 15 October 2001.

  In the same context, mention could have been made of Electro Magnetic Interference (EMI) causing undemanded collective pitch control movements on RAF helicopters, such as when the AFCS Auto-pilot Barometric Altimeter (Bar-Alt) Altitude Hold was engaged, particularly during HF transmissions in the 3 to 15 Megacycles band. (Item 7—Report Addendum 2 on EMI.) I could have also mentioned a well documented case of interference with flying controls in Northern Ireland, when the Infra Red (IR) Countermeasures System (IRCM) Jammer was switched on (and also off?) (Item (11)(a)—Report Addendum 2 on EMI).

Captain Ralph Kohn FRAeS

Also for Captain Ron Macdonald FRAeS and Captain Richard K J Hadlow FRAeS

22 October 2001

October 2000 Flightfax: US Army Safety Magazine

CH-47: A LOOK AT CURRENT ISSUES

  Uncommanded flight-control inputs: This is an ongoing issue within the community that has yet to be resolved. Numerous investigations have been conducted, but none have turned up conclusive evidence of the cause of any of the reported incidents. ASAM CH-47-97-ASAM-01 (151327Z Oct 97) and CH-47-99-ASAM-02 (161228Z Feb 99) have been issued to address suspected causes, and to ensure the proper operation of the aircraft systems. Units should comply with the published messages, and conduct all maintenance procedures by the book. If any flight control anomalies are experienced they should be documented thoroughly and reported through safety and maintenance channels.

  Hydraulic System purification: Historically the CH-47 flight Control Systems have never been serviced or the filters changed unless there was a maintenance problem requiring action. The fact that the systems were never serviced was highlighted during the investigations that tried to determine the cause of the uncommanded flight-control inputs reported from the field. CH-47-99-ASAM-02 (161228Z Feb 99) requires the purification of all aircraft flight and utility systems, and CH-47-00-ASAM-03 (012043Z Jun 00) details the sampling and reporting procedures. This purification and reporting is designed to: remove contaminates (water, particulates, air, solvents), improve system performance, extend fluid life, and establish a baseline for future investigations.

From US Army Report—UFCM (Chinook Rolls through 360º)

SIOCC—QP—AIUSASC 97—305

RECOMMENDATIONS

  1.  CH-47D helicopters are experiencing uncommanded oscillations, flight control movements, and flight attitude changes that may be related to the performance of the upper boost actuators (EIR M16H90214—Panama, EIR M17H90021—Ft. Lewis, WA and this report). Three primary upper boost critical areas are metal contamination in the control head, dead band travel distances, and side loading discovered in the end caps. Army Troop Command (ATCOM), Boeing Helicopter, and US Army Safety Center should establish a combined effort to compare the similarities found in these 2 EIRs listed above, this report, and other similar unresolved incidents. One similar failure, between the Ft. Lewis EIR and this report, was the dead band adjustment, exceeding the normal setting by approximately 83 per cent. This will not be a simple task, because the anomaly occurs, then returns to normal operations on a test stand or in the aircraft.

  2.  An additional critical area is the integrated lower control actuators (ILCA). The metal contamination and moisture found in the pitch, roll, and yaw ILCAs, are considered critical to FLIGHT SAFETY. The amount of contamination found in the pitch and roll ILCA were considered sufficient to cause a disturbance in the normal operation of these components at any time. One solution may be to establish a drain point for each system 2 ILCA, since the corrosion and moisture contamination appears to be primarily found in system 2. CCAD shop personnel reported that some ILCAs arrive with secondary valves jammed due to internal corrosion. This means the unit is operating on the primary control valve with no back-up or secondary valve available. If the primary valve jams, in this situation, the capability to direct hydraulic fluid flow ceases.

  3.  The upper boost actuators and ILCAs deserve immediate and positive action, since these two areas are CRITICAL TO FLIGHT SAFETY, PERSONNEL SAFETY, AND EQUIPMENT SAFETY.

  4.  During aft swivelling boost removal, maintenance personnel discovered that the plain press bushing, P/N NAS75-4-008, Item 142, Figure 376, TM 55-1520-240-23P, was not installed (Encl. 1, Exhibit #42). The parts manual shows the placement of this bushing, but the maintenance manual TM55-1520-240-23-9, Task 11-267, does not address the requirement for the bushing. Installation procedures show the requirement for two washers and not the required bushing. Without this bushing installed, uneven loading is placed on the bolt and clevis. Uneven loading and missing bushings have proven in the past to be directly related to fatigue failure. A note indicating the requirement for these bushings should be added to Task 11-267. (DA Form 2028 has been submitted by the Accident Board Technical Inspector.)