Caravelle's passenger door mechanism is repaired - Part 1

Suomeksi

Until now access to the Caravelle’s cabin has been through the small right-hand side service door and aft stairway. The passenger door operating mechanism has been damaged, and the door can’t be used before the mechanism is repaired. This blog describes the first phase of the passenger door repairs.

When the passenger door is opened, it moves first straight inwards and then it is manually lifted along its rails up to the cabin ceiling. The door weighs 53 kilos, so opening and closing is assisted with a counterbalancing system. The system consists of roller chains, steel cables and three bungee cords (rubber ropes), several metres long and located under the cabin floor. There are no spare parts available for this system anymore, so the new parts have been designed and made by the technical team.

On its visit to Turku on April 12th, the technical team started the door mechanism repair work. The first phase was to install the new roller chains into the door rails (the broken chains had already been removed). The new roller chain is slightly different from the original one and some parts for it were made by order in a laser cutting company, and others ordered from abroad.

When the two roller chains were in their rails, their lower ends were fastened to the brackets on the passenger door and their upper ends to the counterbalancing cables. The roller chains and cables run through the door rails and down to the guides, which are located on the sides of the right-hand side service door. There are 4 guides on each side of the door.

Under the cabin floor, in the side tunnel of the baggage compartment, the cables are connected to the bungee cords on a sliding carriage. The sliding carriage and its stops allow the bungee cords to operate in sequence, as the need for counterbalancing force depends on the position of the door. When closing the door, in the beginning the strength of one bungee rope is sufficient for the required counterbalancing. When the door moves downwards on the rails and is reaching its vertical position, the need for counterbalancing increases. This is when the two other bungee cords join in. The mechanism is complicated and not very reliable. When the Caravelle was in operation, the system needed regular repair and maintenance. The original bungee ropes have become brittle and can’t be used. The technical team is still looking for suitable material to replace the original ropes as the bungee ropes in the regular hardware store are too soft and slack for the purpose.

At this point the roller chain and the door function were tested without the bungee ropes by fastening the cables and the sliding carriage to a manual winch.

It was not that simple to operate the winch in the cramped space under the floor. The lifting force was measured with the digital scales connected to the winch. The original bungee ropes and their supporting rollers can be seen on the upper right corner of the picture.

The test arrangement worked: using the winch the passenger door could be opened, but not fully. At this point the door was secured with a couple or car tyres in the doorway.

The problem appeared to be the roller chain and cable guides, located on the sides of the service door: the new roller chain didn’t move smoothly through the guides. After some discussion the team decided to disassemble and adjust the guides. As a test, the upper guide was disassembled and cleaned, and installed back into place a little bit differently. This helped to solve the problem, so the other guides will be disassembled before the next visit of the technical team when the door mechanism repair will continue.

During the day there was also other activity in the Caravelle: three new instruments were installed into the instrument panel on the flight deck. It looks quite good already but there will be some more additions later.

Photo by Jouko Tarponen.

The cabin curtains were unfastened from their popper slides to have them out of the way when the interior work begins. Fortunately the curtains are mainly in quite good condition, but dirty. They will be washed and ironed before putting them back. This won’t be done before the interior work has been completed.

Photo by Jouko Tarponen

Work was going on outside, too: the SAS prints were removed from the aft stairway before repainting. The best work method has proved to be to heat the painted area first with a blower and the scrape the paint off.

Photos by Erja Reinikainen except if otherwise mentioned.