Since the last report further good progress has been made by the Aircraft Restoration Company (ARCo) engineers at Duxford on the ‘Major’ maintenance programme for BBMF Lancaster PA474, although this is less obvious. A large amount of off-aircraft work has been carried out, with more than 80 components undergoing bay maintenance, mostly with ARCo but some with external sub-contractors. Bay maintenance of the Lancaster’s major hydraulic components, such as the four undercarriage retraction jacks, four bomb door jacks and numerous valves, has been completed by ARCo.
In the previous update we reported that a significant amount of non-destructive testing (NDT) of airframe components was due to be carried out. This NDT work has had to be conducted overnight due to the X-ray hazard and is now almost complete. Included in the testing is work which will provide assurance that the Lancaster’s wing spar reinforcing plates and shackles, which connect the inner centre portion of the wing to the outer wings, are in good condition and fault free.
The task of removing and replacing the control rods for the Lancaster’s elevators and rudders is ongoing. This was the reason for splitting the rear fuselage at the transport joint just aft of the mid-upper turret mounting. The new bearings are being checked by ARCo’s Quality Inspector and, when they are released, the control rods will be refitted.
A large number of chains, tie rods, cables and sprockets run from the Lancaster’s cockpit to the wing front spar and then out along the inside of the wings to control the engines; a similar system, running via the rear spar, controls the ailerons. Historically, these components have been visually inspected during zonal checks, but more than 50 percent of the systems cannot be seen when in place on the aircraft. The new Major maintenance schedule now calls for these cables and chains to be removed and inspected, something that has never been done before on PA474. The first batch of 10 chains has been removed for inspection and this work is on-going. Any items deemed unserviceable will be replaced with newly fabricated items using the correct chain type and link pitch.
During the airframe inspections, damage to some of the Lancaster’s starboard trailing edge wing ribs was found. The damage is hard to spot as it involves displacement of the rib itself (in the outboard direction) caused by misalignment of the flap tube. The misalignment was caused by a flap actuating rod ball joint seizure where the flap tube connects to the flap jack assembly (actuator) at the centre section. The flap tube has been disconnected, and the starboard inner flap has been removed. The flap tube has been checked on a surface table and is not misaligned. The inner trailing edge of the starboard wing has been removed and ARCo has identified a repair which could be used to rectify the damage. The proposed repair has been submitted to BAES’s Structures Subject Matter Expert via the BBMF Project Team’s EA4 team and a response is awaited from BAES. In addition, several riveted wing skin access panels have been identified as being beyond repair and new panels need to be manufactured.
