Wide-body MRO hangars

How does Wide-body MRO hangars work, step by step?

1. 1

   Step 1: Fix the geometry from the operator's brief

   The first move is agreeing the clear volume: the width and depth of the column-free area, the clear height at the tail position, and the door opening that follows from both. That comes from the operator and the designer working through the aircraft the building has to accept, how they will be positioned, and what has to fit around them. Docking, staging, stores and plant all take space that people forget at the sketch stage. On most projects the geometry is locked before any structural scheme is priced, because every later decision - span, frame type, door type, foundation loads - is downstream of it.

2. 2

   Step 2: Choose the structural scheme and the door together

   The frame and the door are one problem. The designer tests schemes against the opening: a deep header truss over the doors with the roof spanning back to it, portal frames with a braced rear, or a truss roof on stiff end walls. Each option changes the door type that can sit under it and the deflection the door supplier will accept. The door supplier is brought in during design rather than after tender, because their loads, rail levels, headroom and tolerances feed straight into the frame. This is the single most common place these projects go wrong: a frame designed in isolation and a door package bought later that cannot live under it.

3. 3

   Step 3: Found the frame and the door rails

   Long-span frames concentrate very large loads into a small number of positions, so foundations are heavier and fewer than on ordinary industrial work, and horizontal thrust at the base often governs. The door runway is a separate foundation problem of its own: it is a long, straight, level track that must stay straight and level, and it usually sits right at the interface between the building and the apron, where ground conditions change. The designer decides how the runway is founded and how it is isolated from apron movement. Setting out is checked and re-checked before any concrete goes in, because a door rail is not something that can be adjusted afterwards.

4. 4

   Step 4: Erect the long-span frame

   Erection of a long-span roof is a temporary works project in its own right. Trusses are commonly assembled at ground level in bays and lifted in whole or in large sections, which means big cranes, planned crane positions, ground bearing for those positions, and a lift plan agreed well in advance. The frame is unstable until enough bracing is in, so the sequence is designed rather than improvised, with temporary bracing and props specified and left in until the permanent restraint is complete. Working airside adds its own constraints on crane heights and on when lifts may happen, and those are agreed with the operator before the programme is fixed.

5. 5

   Step 5: Install and commission the doors

   The doors arrive as a kit of large, heavy components and are assembled on the rails. Alignment tolerances are tight and the survey is continuous: rail level and straightness, leaf plumb, seal contact, and the clearance under the header once the roof has taken its full load. Deflection of the header between erection and completion is allowed for rather than discovered. Commissioning covers drive systems, interlocks, wind locking, manual release and the safety devices, and it is witnessed. On most projects the doors are proved through repeated full operating cycles, because a door that works once and binds on the tenth cycle has not been commissioned.

6. 6

   Step 6: Cast the serviced floor

   The floor is set out around the aircraft position, not around the building grid. Pits, trenches, ducts, drainage and any jacking or docking bases are fixed and surveyed before the pour, and the slab is designed for the concentrated wheel and jacking loads the operator states. Flatness matters because docking and access equipment has to assemble and roll on it. Joint layout is planned to suit the loading and the traffic patterns rather than left to the pour sequence. Drainage runs through interception, and the falls have to work with a floor that also has to be flat, which is a detail worth resolving on paper first.

7. 7

   Step 7: Fit the docking, cranes and dropped services

   Docking systems and access platforms are installed and set against the actual as-built floor and structure, and this is where earlier tolerance failures surface. Overhead cranes, hose reels, extraction, power and lighting are hung from the roof at the positions the operator needs, using the load allowances agreed at design stage. Fire protection is installed to the fire engineer's design and commissioned under their direction, with the authority satisfied before the building is used. Nothing about that system is standardised across projects, so it is designed, installed and proved for the specific building.

8. 8

   Step 8: Prove the building and hand it over with its manuals

   Handover on a hangar is heavier than on ordinary industrial work because so much of the building is machinery. Doors, cranes, docking, fire systems and the airside services are all commissioned, demonstrated and documented, and the operator's staff are trained on them. Maintenance regimes for the doors in particular are set up on day one, because the doors are the item most likely to fail in service and the one whose failure stops the operation. Record drawings of pit and service positions matter for years afterwards, since the next docking system or the next aircraft type will be set out from them.