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B737-Classic

ENGINEERING

CONTINUATION TRAINING

Q3 & Q4 2013

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Contents:

1 Introduction 2 MOR Listing 3 ADs 4 ACL Engineering Notices

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1 Introduction The following relates to the B737-3/4/500 Series aircraft type.

2 B737 MOR Listing The following are maintenance related MOR from the UK CAA MOR digest. As the information is protected and strictly controlled by the UK CAA, it is respectfully requested that this information is not circulated. Jet 2 B737 Pylon access panel found to be missing. A passenger noticed that there was a 'hole' in the top of the RH engine. On investigation it was discovered that a pylon access panel, not visible from the ground, was missing. Aircraft despatched according to the Configuration Deviation List. Jet 2 B737 Forward hold extinguishing nozzle was found with all holes blocked after being painted over. AFT hold nozzle had approx 50% of holes blocked by paint. The holes were unblocked post inspection to allow the system to be serviceable. Investigation under 201304794. British Airways B737 Elevator tab control rods incorrectly assembled and not wirelocked. During inspection, it was found that the check nuts were not wire locked on either control rod, on both LH and RH elevator tabs. Additionally, the 'Hi-Lok' heads were incorrectly installed on the control rods, in the opposite positions. Rectification action has been taken and the operator and manufacturer informed. Jet 2 B737 Captain's stabiliser control wheel loose on spindle. Further investigation found that both control trim wheels were incorrectly installed. Both were in line with each other but did not have a 90deg split. The wheels had also been transposed. Both wheels removed and re-installed correctly. Titan Airways B737 Spoiler cable failure. During inspection of the LH main undercarriage wheel, the flight spoiler control cable was seen to have completely failed at the point where it exits a pulley block. The cable running next to it was frayed almost to the point of failure. Both cables and the pulley were replaced.

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Jet 2 B737 Nr4 slat auxiliary track bearing worn. During inspection, the nr4 slat was found to have excessive movement on its inboard side. When accessed, the auxiliary track bearing broke into three pieces and the bolt was heavily grooved. The complete assembly had to be replaced. CAA Closure: During the previous C-Check several spoiler defects were found but no No.4 Slat defects were found. This check is carried out every 250 Flight Hours to ensure these issues are picked up by maintenance before an event. Therefore the system can be stated as being effective and can be regarded as a preventative maintenance action. Jet 2 B737 MAYDAY declared and emergency descent carried out due to rapid depressurisation. During normal descent from FL360 to cleared level of FL310, the 'RH bleed trip off' light illuminated. QRH was called for but before it could be actioned, the 'LH bleed trip off' also illuminated. Cabin rate of climb was significant and pressurisation was confirmed as uncontrollable, the cabin altitude warning horn sounded. MAYDAY declared and an emergency descent was initiated. QRH drills were performed during the descent and the aircraft was levelled at 8000ft. ATC stated that the pilot was wearing an oxygen mask. All passengers and crew were safe and well throughout and the aircraft landed successfully. CAA Closure: Dual bleed trip attributed to three component failures, on the right hand side a pre-cooler control valve failed at 45deg closed. On the left hand side a cracked pre-cooler operating at lower than normal efficiency and a out of calibration 390deg pre-cooler control valve sensor sending a spurious sense to shut the otherwise normally functioning left hand PCCV thus reducing cold airflow. Currently operator carries out Single Pack Confidence Checks post heavy maintenance. Operator now intends to also carry out Single Pack Confidence Checks out at SC7 where appropriate. Pre-coolers currently soft lifed at 4C (due 2017 on this aircraft). AMP to be adjusted to replace pre-coolers at every 2C. Currently the pre-cooler control valves are set at the aforementioned 4C interval. AMP to be adjusted to replace both pre-cooler control valves and pre-cooler control valve sensors at 2C. Jet 2 B737 Loud droning noise and excessive vibration during initial and further climb on high thrust. A/c diverted for engineering assistance. Noise and vibration reduced as a/c levelled at FL190 when thrust could not maintain 250kts. All engine instruments showing normal indications during take-off and further climb. Previous flight had reported noise which was reported in Tech Log. Once decision made to divert a/c entered hold to burn fuel to reduce landing weight and nr1 engine vibration gauge reading increased up to 2.5 units at 230kts, approx 60% N1. Noise and airframe vibration increased when thrust increased to intercept glideslope. CAA Closure: Load drowning noise and airframe vibration during initial climb and further climb when on high trust. The noise and vibration reduced as aircraft levelled. All engine instruments showing normal indications during take-off, initial climb and further climb. This noise was experienced on the previous flight and reported. This was cleared by engineering as a loose wing fairing. On this occasion, inspections confirmed that the noise and airframe vibration was caused by nr1 engine blades 5/6 and 32/33, which were found to be shingled. Blades untangled and inspected satisfactorily and ADD raised to remove affected blades for shop inspection, prior to 50cyc extension limit.

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Jet 2 B737 Engine with intermittent high EGT found to have bolt missing which connects master bleed valve to bleed valve motor. Engine was sent for maintenance investigation with intermittent high EGT. During inspection of the exterior of the engine it was discovered that a bolt connecting the master bleed valve to the bleed valve motor was missing. Lock nut on the fork end of the control rod/arm was found to be loose and had not been safety wire locked. CAA Closure: The aircraft and engine history was reviewed and during the last 'C' Check Oct-Dec 2012 it was found that VBV feedback rod had broken clevis and master bleed valve actuator had broken feedback lever. The damaged bleed valve actuator was investigated and subsequently concluded that it was a one off incident possibly due to a manufacturing defect within the parts concerned. The engine manufacturer were consulted at the time and stated that there had been no previous incidents of the shaft or actuator breaking. Further review of the aircraft history did not confirm why the bolt was missing from the feedback rod/reverser arm connection. There could be an assumption that the bolt may have been removed by mistake, but there is no evidence to support such a theory. It has been stated by the operator that while the engine is on the current shop visit, the operator has requested that the fuel gear motor and MEC are replaced in addition to the repair of the HPC. The engine will also be run on the test cell to ensure that the EGT problems are resolved. The replacement of the gear motor and the MEC is the final step of the 71-00-42-101 fig. 104 troubleshooting procedure. British Airways B737 Gear would not retract after take-off. A/c returned. A/c had departed following repair to an air/ground pressurisation sensor fault. CAA Closure: The initial defect manifested itself as the aircraft was going into air mode whilst taxiing out. Troubleshooting for this event pinpointed the S105 switch as defective. This switch is in a hostile environment and there are no practical tests to measure drift or ohmic drift as preventive measures. The switch was replaced, function tested and the aircraft declared serviceable. On the subsequent departure, the aircraft remained in ground mode when airborne and the aircraft returned. Interchanging the air ground logic cards transferred the defect, so it was concluded that the card was defective. This card was replaced, the systems tested and the aircraft declared serviceable. On the subsequent departure, the aircraft had a hybrid situation of system availability as though the aircraft was trying to operate in both air and ground modes. Again, the aircraft returned. Detailed investigation revealed damage to the edge connector on the E11 rack, which caused intermittent connection and system malfunctions. The defects to the E11 rack were rectified, systems tested and the aircraft departed with no further incident. British Airways B737 Cargo door opened on touchdown. Forward cargo door warning light illuminated on touchdown and ground crew reported that the forward cargo door was open as the a/c pulled onto the stand. Engineers attended the a/c and investigation found that the interior handle had no resistance and was free to drop down and rotate freely, causing the latches to release the door. The large spring attached to the handle was found to have sheared and detached from its anchor point. CAA Closure: Investigations found that the reason for the forward cargo door opening was a sheared interior door handle spring. The failure of the spring causing the cargo door to open when the aircraft is unpressurized is a known condition. The failed spring was of the type (Post SB) designed to prevent occurrences of this nature.

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This is the first report Boeing has received of a failure of the improved spring design. Boeing has the sheared spring in their laboratory for analysis but have still to complete the analysis and have not yet identified the root cause of the failure. Boeing has determined that the spring failure and subsequent cargo door opening in flight (door is plug type and opens inwards) does not meet the criteria for a potential fleet safety concern. Jet 2 B737 A/c de-pressurised, MAYDAY declared and oxygen masks deployed. A/c diverted and landed safely. No reported injuries to crew or passengers. On arrival on stand, an external inspection revealed that the rear cargo door seal was detached around the lower left corner. CAA Closure: This was caused by a clip that is part of a previous modification in which a strap is secured around the open cargo door to prevent the door coming down. On the door closing operation the clip got caught on the seal and pulling it partially away. As the seal was detached the aircraft was able to sustain cabin pressure (although leaking) until the differential pressure was enough that it blew the seal out through the cargo door and thus allowing a greater outflow of cabin pressure. Operator has raised a modification to remove clip from cargo hold. MOD-AES-737-2867-Part-21. Modification resulted in the Cargo Door Cables and Pulleys having to be replaced in order to remove the Straps. Modification to remove straps is an ongoing process with some already having been accomplished. Jet 2 B737 Emergency descent and a/c returned due to loss of cabin pressurisation. While checklist was being actioned, it became clear that the cabin rate of climb was uncontrollable so checklist suspended and an immediate descent was initiated. At approx FL120 the cabin altitude warning horn sounded and flight crew donned oxygen masks. CAA Closure: The lack of pressurisation was a combination of chaffed and broken wiring controlling the Right High Stage Valve & associated Regulator which caused insufficient pneumatic feed. Wiring repaired IAW SWPM 20-10-13. Operational test of cabin pressurisation system carried out. R/H Pre-Cooler control valve replaced IAW AMM 36-12-35. High stage regulators transposed to aid trouble shooting. A single pack pressurisation confidence check carried out IAW AMM 21-00-05/201 and found satis. R1 door seal & frame cleaned & seal adjusted. Cabin pressure leak rate carried out IAW AMM 05-51-91. Leak rate from 4.0 PSID to 2.5 PSID within 100 secs. Aircraft considered serviceable. Further preventative actions; The pre-cooler control valve replacement interval has been halved (along with other associated bleed air components) and the cabin pressure confidence check work card has been revised to inspect for the APU pneumatic pressure seals; In addition the operator has created specific task cards to inspect wiring in areas over and above the MPD. A continual review of inspection findings will be part of the process. Also Engineers will be reminded that if they are in an area to be vigilant for wiring defects, for example, signs of chaffing, arcing, excessive debris, correct routing, correct support, crimp connections etc. Also the operator has stated that it will carry out a review of electrical issues and determine what level of specific training to all Engineers on these kinds of issues is required.

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Jet 2 B737 Rear attachment bolts for the dorsal fin not fitted. During C Check inspection of the vertical stabiliser it was found that the two rear attachment bolts for the dorsal fin were not fitted. This had allowed the shims to move and as a result allow misalignment of the dorsal fin. The access to install the bolts if from the cabin above and behind the 4B galley. A job card has been raised and has been staged to ascertain if the bolts have fallen out or ever been installed, and the condition of the anchor nut for resistance. Jet 2 B737 Hydraulic leak due to damaged pipe. The crew reported that flap 5 would not run when selected. They recycled them several times and eventually they ran out to flap 5 successfully. On investigation we carried out visual inspection of the flaps without finding anything unusual. I then carried out an operational test of the trailing edge flaps iaw AMM 27-51-00. The first part of the test was carried out successfully but during subtask AMM 27-51-00, which tests the alternate part of the system, we noticed a large hydraulic leak coming from the area around the outboard leading edge flap on the right-hand wing. When we removed lower wing surface panels 6405r and 6404r we discovered the leak was coming from the flaps down standby hydraulic pipe. On further investigation we found that the leak had been caused by a engine bleed duct clamp bolt located directly above lower wing surface panel, forward of the inboard front spar rubbing against the pipe. If the engine bleed clamp had been rotated to a different position this problem could have been avoided. British Airways B737 Nr4 LH ground spoiler panel fluctuating on landing. A passenger reported that the spoiler panel was fluctuating on landing. Investigation found that both actuator hinge brackets had failed at the bearing attachment points and both outboard hinge fittings were extremely worn. CAA Closure: The failed parts were not retained for examination, and thus it has not been possible to determine the exact failure mode. From the description of the damage provided it conforms to a known failure mode for which improved parts are available and an inspection programme exists. British Airways B737 PAN declared due to loss of 'SYS A' hydraulics. Shortly after stowing speed brake, low pressure light and gauge indicating zero hydraulics. PAN declared and QRH actioned. Requested 15nm final at 3000ft and landing gear manually extended at 13mn. Aircraft landed safely with emergency services in attendance. CAA Closure: The organisation has concluded its investigation. The root cause (failure of the body of the nr1 spoiler actuator) is an understood phenomenon. Short of a campaign removal for modification there is very little that can be done to prevent failures of this nature. Modified units are not displaying any significant increase in reliability. It is not possible to procure the pre-mod actuator body from the OEM, so should this unit be deemed to be not beyond economic repair it will be modified by default.

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Pre-mod and post-mod actuators are interchangeable and intermixable, and there is no difference in maintenance requirements for either unit. The QRH procedures are effective in the event of total hydraulic loss, and the aircraft is controllable manually with no hydraulics. This incident is therefore classified as not significant from a safety viewpoint. British Airways B737 On arrival nacelle/pylon panel found to be missing. CAA Closure: The conclusion is that the panel was removed and not refitted correctly. Panel fitted correctly. A manual amendment has been raised to have panel 463AL (plus the equivalent panels on pylons 1,3 and 4) added to the task list and AMM so that they can certify as removed and refitted on the engine change sheets. A performance diary and a factual letter recording the incident has been placed on the quality file of the engineer who certified the precooler panel removal, pneumatic disconnect and subsequent reconnect. A performance diary entry has been made for all relevant staff to record their involvement in this incident. British Airways B737 On vacating the runway 'A' system hydraulics decreased to zero. During taxi nosewheel steering unreliable. A/c stopped and parking brake applied. Master caution illuminated but no system light illuminated on master caution panel. Both 'A' system pump lights had illuminated due to total loss of system 'A' hydraulic fluid. Ground ops vehicle advised that fluids were leaking onto LH engine. Engine shut down. Fire services called and attended. RH engine then shut down and a/c towed to stand after QRH checklist actioned. CAA Closure: Failure is fatigue initiating around the minor diameter of the actuator body threads. The failure is such that there is no indication of an issue externally when visually inspected as part of a zonal inspection. The failure mode is a fracture of the actuator body gland nut threads, which results in separation of the gland nut and liberation of the piston. Defective part replaced. British Airways B737 Aircraft significantly out of trim during take-off. Aircraft was trimmed 3.3 units on the elevator prior to take-off. Rotation was extremely difficult. Rear trim was applied until the aircraft was established in initial climb and in trim. Trim required was 5.2 units. CAA Closure: The organisation has concluded its investigation. After many attempts to establish the cause of the various pilot reports (inc the one referenced here) the defect was traced to damaged bearings in the elevator input shaft torque tube. The torque tube was sent to workshop for bearing replacement then re-fitted. The aircraft returned to service on 27th September, operating a maintenance check flight with no issues. There have been no further reports of elevator issues since. British Airways B737 Mandated Service Bulletin instructions for repair not carried out.

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Following a review of the subject aircraft, returned feedback form for SB737-53A1279 Inspection of Wire Penetration Hole on Frame 500R mandated by FAA AD 2011-23-05 detailed a recorded crack of 5mm in the frame reinforcement which was removed by a blend of 0.020in. This raised concern because the amount of removed material would not cover removal of the recorded crack. Following further investigation no evidence of SRM 53-00-07 Repair 13 embodiment was found. The AD mandated SB does not permit blending of the frame or reinforcement but instructs that if a crack is found carry out repair iaw SRM 53-00-07 Repair 13 was required. Defect cards were requested and following the conversation with the maintenance organisation they agreed to carry out Repair 13 prior to release to service. This also highlighted a possible compliance issue with the previous input aircraft and the feedback data and defect cards were requested for the operator technical department to review. They were supplied and this also highlighted a crack was found and blended which does not meet the requirements of the mandated SB. Inspection of the aircraft was carried out on completion of the operational day. Engineers inspected the frame and provided photos which indicated the repair was also not correct. Engineers will action the requirements of the SB by actioning the SRM 53-00-07 Repair 13 to maintain correct compliance of the AD and SB. Reporter suggests that any new MRO facility operator chooses to maintain registered aircraft are audited for task cards including mandated repairs to ensure the MRO meet SB and AD requirements. CAA Closure: The certifying engineer failed to follow the instructions within the SB which required the AD requirements to be applied to any cracking in the frame or replacement angle. The investigation concluded the root cause of the incident to be complacency on the part of the certifying engineer carrying out the task, with a key contributing factor being a failure to use all available maintenance data. Outcomes were: 1. Engineer was appraised of his mistake and reminded to fully read all maintenance data. 2. Safety & Compliance Bulletin issued highlighting the need to read and understand all maintenance data. 3. Structures Team have initiated a handover diary system in accordance with company procedures. 4. Systemic review of handover diaries being performed. Jet 2 B737 Ground spoiler attachment bolt found not securely installed. During inspection, it was observed that the nr9 ground spoiler to spoiler actuator bolt was installed with the nut wound on by only 3-4 threads. Had this gone unnoticed there is a possibility that the nut could have become detached from the bolt resulting in control issues. Parts checked and re-installed to the correct torque value. CAA Closure: Investigation of Tech Log pages from the previous 12 months showed that work was carried out on the RH outboard spoiler and spoiler system during the previous C Check at a foreign maintenance organisation. This Service Check 1 was the first one since the C Check. The ground spoiler attachment bolt was subsequently securely installed and checked. Discussions between the operator and the maintenance organisation were held concerning the investigation. it was found that the maintenance issues are recognised and large changes to the management and control of staff have been implemented. It was found that the Maintenance Manager was moving engineers from aircraft to aircraft to try and meet the demands of customers. This practise has been curtailed, with a new Maintenance Manager having being brought in and the practice of working on more than one aircraft is now against the MRO’s policy.

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Jet 2 B737 Smoke in Flight Deck After engine start overhead panel light selected on, subsequent to switching on smoke was seen from the wheel well switch and the top of the overhead panel. Lights turned off and smoke dissipated, aircraft returned to stand. On subsequent pushback, overhead lights switched on and smoke emanated from overhead wheelwell and top of overhead panel. Panel switched off and smoke stopped. Fault traced to lower P5 panel lighting control panel. Lightplate panel internal short circuit. Jet 2 B737 Stabiliser trim wheel retaining nut loose. During pilot pre departure check it was found that the Captains stabiliser trim control wheel was disconnected from the shaft, the retaining nut had come away completely and was on the flight deck floor. No spares in stock to replace nut so decision made to rob one from another aircraft. On checking the stabiliser trim wheel of the second aircraft it was again found that one of the retaining nuts was also loose. Jet 2 B737 Restricted movement in rudder pedals. During control checks, it was noticed that extra force was required to move the LH right rudder pedal more than half way along its travel. After several movements it was moving fully and the a/c was dispatched. On arrival, the same problem occurred and an engineer was called. Inspection found that an incorrect bolt had been installed in the LH rudder pedal assembly causing the restriction. A/c out of major maintenance by 2hrs. CAA Closure: Initial investigations concluded that the screw(s) attaching the rudder pedal fairing were incorrect and that they were too long. Follow up investigations concluded that it was the use of clip nuts, whereas the IPC denoted screw and nut in the fairing panel attachment. It has been found that the IPC only allows the use of standard nuts and bolts/screws (or cam lock) in that area. The clip nuts extended into the channel that the rudder pedal mechanism travels and are being used to make the task of holding the nut in place easier. Due to this issue occurring on more than one aircraft, a task was raised to inspect the area across the fleet and includes the recording of the fastener type used. The MRO has highlighted this issue in recurrent training as well as making all engineers aware. Jet 2 B737 RH high stage valve stuck in closed position. ADD was raised for the RH high stage valve stuck in closed position. After inspection of the valve, the locking bolt which is used to lock the valve in the closed position was sheared and the valve was in the unlocked position. MEL states the valve must be locked in closed position for dispatch. A glove was also found in the engine, forward of and above the valve. CAA Closure: During Climb (and full reverse thrust during landing) the RH duct pressure indicated 80PSI with all indications normal during cruise/descent. Pressure regulator shutoff valve and regulator bleed air outline replaced and tested satisfactorily. During inspection, high stage valve stuck in closed position and impossible to turn. Aircraft dispatched iaw MEL 36-03 and ADD raised. Nr2 engine high stage valve replaced after next flight and tested satisfactorily. This unit was found in the open position with the locking bolt sheared. If open during the high power phases of flight, excessive hot air will enter the ducts leading to issues with the pressure packs. No issues occurred during the return flight, indicating that the unit was not stuck open for the entire flight but had failed prior to being fitted. Subsequent strip report found actuator cover damaged, this being the primary failure.

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A bolt was found sheared which contributed to the shaft seal assembly leaking. A seized thread in the manual lock securing screw can cause the screw to be broken off.

3 B737 Airworthiness Directive Listing 2013-15-14 Slat Track Hardware

2013-24-13 Seat Track Links

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4 B737 Engineering Notices (ACL) EN Ref: Description 002/14 Speedbrake Lever Switch Controls

EN Ref: Description 003/14 Revision to SRP

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EN Ref: Description 015/13 Latching of Engine Cowls

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EN Ref: Description 016/13 Main Wheel Tyres

EN Ref: Description 019/13 Wheel & Brake Unit Part Numbers