Heritage Concorde

The Engineering Maintenance Operation

 

Where Concorde is concerned, cost was always uppermost in the mind. Not only were its maintenance man-hour costs about four times that of a Boeing 747, each spare part had a similarly inflated price tag due to the fact that only a few aircraft were flying and purchase costs were artificially loaded by the governments to enable it to recover some of the large expenditure incurred in building the aircraft. Even so British Airways achieved the seemingly impossible, by managing and operating Concorde at a profit. Another significant aspect with regard to engineering were the compexities inherent in an aircraft which was in 2003 more than 27 years old. With all the superlatives heaped on Concorde, it seems rather strange to label it as old technology, but such it was in spite of it state-of-the-art features which include fly-by-wire.

Maintenance was a complicated procedure and when technical problems accured, they also tended to effect the whole fleet at the same time, requiring particular attention and increased effort. The same engineers, therefore, looked after the aircraft from the moment  it arrived on the ramp to it’s actual departure, and thus this generated a tremendous relationship with the technical crews and other, non-engineering, staff.

Concorde engineers had been responsible for well over 300 modiifications since the aircraft entered service. The great majority of these had been carried out to improve reliability – especially despatch reliabilty, which averaged with British Airways 95% – appearance and passenger amenities. The operational service of Concorde speake volumes for the skill and dedication of the engineering team.

Concorde was the only aircraft for which the Maintenance Divisions carried out the full maintenance operations from minor servicing to major overhauls. As is the case for every aircraft, there is a maintenance schedule stipulating the frequency and content of each check. This schedule is defined by the manufacturer and the operator, and then submitted to the British and French Civil Aviation Authorities ( CAA & DGAC) for approval.

Concorde had to have the following checks:

 

ENGINE MAINTENANCE & CHECKS

 

The Olympus 593-610 engine was a tough, hard-working aircraft engine, yet it was so highly tuned as to squeeze every last ounce of efficiency from it.

It was unique. There was nothing to compare it; there was nothing to compare with it.

In service its reliability was good-very good: the checks were varied to monitor the engine health, to intercept a problem before it arose and for preventive maintenance.It was broken down into five headings: SOAP, MCD, EGT, oil consumption and borescope.

SOAP – SPECTROGRAPIC OIL ANALYSIS PROGRAMME

Every 50 flying hours oil samples were taken from each engine, at Heathrow, within 2 hours of shut-down and before replenishment. Simples were dispatched on a daily to a company at Fairoaks in Surrey for the same-day laboratory analysis. Initially, the samples were scanned for traces of iron, magnesium and silicon, the units of measurements being parts per million (ppm). Should any of these elements exceed its alert level by a particular amount, then the Magnetic Chip Detectors (MCD) were analysed and considered in conjunction with the spectro results before the engine could continue in service. Whatever an alert was met, a recurring requirement was raised directing a spectro and MCD check at every return to base. Thus critical decisions on engine serviceability used both sets of evidence.

MCD – MAGNECTIC CHIP DETECTORS

The Olympus has three magnetic Chip Detectors and a specialist group to analyse them.  The three MCD’s were strategically placed within the engine as follows:

In the left-hand gearbox scavenge filter trapping debris from the thrust bearings (2 and 3) and the left-hand gearbox.

In the right-hand gearbox scavenge filter trapping debris within the right-hand gearbox.

In the main external return-flow pipe. This one designed ‘Master MCD’; it attracted debris from the total system.

Every service checks – 175 flying hours – all three MCDs were removed for deposit analysis. ‘Big lumps’ went under the microscope; a rolled flaky appearance was indicative of a bearing problem, while more granular particle suggested gear of shaft frottage. But it’s the sludge that was most fascinating. To put it another way, reading message was in the ring around the rim.

The sludge sample was bombarded with X-rays. Each chemical element in the amalgam would emit a different radiation. Using a computer, programmed with radiation signature of elements used in engine metals, the analyst would be presented with readout of the detailed composition of the sludge. Moving on a step further, knowing exactly what each engine alloy was made of, and introducing graphics, the sample’s footprint could be compared with known footprints: eg No.1 bearing housing was made from an iron-based alloy, MSRR 6544 – in addition to its base material it had 25% carbon, 14% chrome, 1% manganese, 1% nickel and 0.8% silicon. Having matched the footprint, one could point fairly precisely to the assemble under suspicion.

It was well known that a newly installed engine would generate a relatively high level of debris as shafts, gears and bearings bedded-in and grease, used in engine build, washed down-grease raises the silicon content.

Nevertheless, the checks remained. An engine must demonstrate three consecutive good checks before removed from the ‘alert’ file.

EXHAUST GAS TEMPERATURE (EGT)

The combustion chamber, even in its latest incarnation, still took a battering from the high energy gas flow. Deterioration, before becoming damaged would still upset temperature patterns, and to catch a trend before it became a problem had huge benefits.

In 1986 Rolls-Royce devised an EGT trend analysis program to be loaded into a programmable Sharp 1248 hand-held calculator. This became a routine part of the flight engineer’s in-flight tasks. Using real-time data, even the smallest divergence of EGT was apparent; recording and plotting created the trend. Its ‘raison d’ etre’, a raising trend was indicative of a problem within the combustion chamber/turbine area-cooling holes unzipping, vaporizer cracking, hot streaking – 20C up would result to base. A dynamically increasing trend would require a shut-down judgment. A minor reducing trend would result from compressor deterioration (nicks, scratches, erosion etc). Cruise EGT, incidentally would be about 650c

OIL CONSUMPTION

At each station, oil uplift and flight time were assessed to produce a consumption rate; once again recorded and plotted so the trends were immediately apparent.

BORESCOPE

The medical people call it an endoscope. It’s the same minaturised viewing technology. Engines are designed with inspection points in key areas, blanked-off in service, but readily available for either routine internal inspections or ‘alert level’ extras when SOAP, MCD or EGT require.

 

AIRFRAME & SYSTEMS MAINTENANCE

 

Pre-flight checks:

 (before each flight)

Daily checks:

Routine operations and inspections every 24 hours according to checklists

Check A

Routine operations and inspections every 210 flight hours according to checklists. In addition to operations specific to this type of check, Check A also includes the maintenance operations covered in daily and weekly checks.

Check B

Routine operations and inspections carried out every 420 flight hours according to checklists.

Check C

Routine operations and inspections carried out every 1,680 flight hours according to checklists.

Check IL

Routine operations and inspections carried out every 6,000 flight hours according to checklists.

Check D or  major overhaul, sometimes called the ‘M’ check

Routine operations and inspections carried out every 12,000 flight hours according to checklists. This is an extensive maintenance operation which required the total dismantling of the aircraft. Inspections are carried out on the airframe and a large number of parts were systematically replaced. The plane was grounded for nearly one year. The technical monitoring of the engines were carried out on the French airframes  by the Air France Industrial Logistics Branch, using instructions from the engine manufacturers Rolls Royce and Snecma.

 

Check M or  major overhaul carried out on British Airways Concorde G-BOAF between October 1992 & June 1993

 

 

This a report on that major service and overhaul.

This was the longest and most comprehensive check  ever carried out on a Concorde, Alpha Foxtrot spent six months in the TBB’s maintenance dock.  The extended check not only included the routine major maintenance, but also included additional work which would  benefit the entire Concorde fleet and provide additional data for the future of supersonic travel.

Consultations were carried out in conjunction with British Aerospace (Now BAe systems) and Aerospatiale (Now EADS),to facilitate fitting 31 strain gauges to the main stress points on the left wing and the left-hand side of the fuselage. Since airframe testing by Concorde’s manufacturers had ceased in the middle 1980’s. these gauges would be used to monitor loads in the airframe during 12 supersonic services – providing additional data on  airframe life. Alpha Foxtrot would be the only  aircraft to carry  such  equipment and it would be removed after these flights.

The Production Controller Mike Higgins began initials studies into the check list during October 1992, planning out a life extension modifications with the first installation of a Traffic Collision Avoidance System (TCAS) on a Concorde.

Preliminary checks begain on G-BOAF on December 21st 1992, prior to a total shut-down of its electrical and hydraulic systems. System intergrity checks, covering flying control fuctions and hydraulic leaks were carried out along with detailed boroscope checks of each engine. At this point, Production Contoller Ron Rogerson joined Mike to ensure work was fullcontrolled over both early and late shifts.

Following this thourough examination, Alpha Foxtrot was towed off to TBK’s Paint Bay to be stripped of it’s glossy coating. Thus, on January 4th 1993, in virginal grey aluminium, the naked Concorde arrived for an extensive re-work in TBB’s purpose-built dock.

 

In essence, this was a strip-out and re-build with additional comprehensive mod programme. Once it arrived in the dock the aircraft was jacked into place before the strip out in earnest. Pretty much well everything came out – overhead bins, wardrobes, galleys, toilets and most of the floor. Even the cabin wall insulation blankets were removed, leaving a long metal shell.

Part of the fleet’s life extension programme includes strengthing to the fuselage “crown area” – a 20 ft section of roof, spanning from the cabin window to window between the wings. the dorsal fin and elevons were removed for inpection and rework.

Further work included the installation of restrictors to reduce pressure peaks in the powered flying unit selector valves, and a series of modification to reduce stress concentrations. Twelve strain gauges were attached to selected points in the left wing and 18 at the floor level on the left of the fuselage, with one in the trim-tank. These were calibrated prior to a pre-service test flight.

Addionally, following a request from  Boeing, four windows were replaced on the right side of the fuselage with metal blanks containing sensitive micophones. These monitored noise produced by the aircraft’s 2boundary layer” – the thin membrane of slower moving air that forms betwwen the aircrafts skin and surrounding air – during supersonic flight. Such data will aid research into a possible Concorde successor.

On the wings, a series of strengthening mods encompassed both engine bays where small areas of lower wing-skins were shot-peened and thrust balance attachment mounts inpected and re-worked. After removal of the enging bay doors, air intakes, primary and secondary nozzles, thrust-reverser buckets and heat shields, each bay and all-four intakes were completely rewired and every hydraulic pipe removed and renewed.

Once the work on the engine bays was completed, a progreeive re-build began, starting with new cabin insulation blankets in the cabin and replacement of engines on the wings.

By May 6th 1993, the aircraft was ready for its first engine run to test the rebuilt systems, this was remarkably successful. Each of the engines was tested on a series of throttle settings up to full power and there were very few defects. given the complexity of the work carried out, it was a very satisfying result.

Four days later, all access panels being refitted prior to a ful re-paint, and by May 15th G-BOAF, Alpha Foxtrot was ready to face the world again, she was clad once more in gleaming red, white and blue livery. But before its public debut, the aircraft returned to the TBB to be fitted with-out with the new Concorde interior, featuring new seats, larger overhead bins, new galleys, improved toilets, a new inflight entertainment system and new passenger and cabin lighting.