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How flying boats and landplanes of Imperial Airways are kept in first-class condition

ALL PROPELLERS OF EMPIRE FLYING BOATS are thoroughly checked every 270 hours of running

ALL PROPELLERS OF EMPIRE FLYING BOATS are thoroughly checked every 270 hours of running. The blades are examined for scratches through a magnifying lens, and the hub gear which controls the pitch of the blades is dismantled. The steel parts of this variable-pitch gear are tested for cracks by being magnetized and covered with iron filings and paraffin. The filings would form in a heap across a gap and so reveal it.

THE maintenance of the flying boats and landplanes of Imperial Airways’ large fleet is one of the most important sections of the company’s activities. In June 1938 the aircraft maintained in service consisted of fifty-nine aircraft. There were twenty-eight Empire flying boats, the Satyrus, which is one of the older Kent type, and the two flying boats Mercury and Maia, which are the upper and lower components of the Short-Mayo composite aircraft. In the landplane fleet were seven aeroplanes of the Heracles and Hannibal type, two of the Scylla type, five Atalantas, eleven D.H.86s, and three training machines. In addition fourteen Ensign air liners and five De Havilland D.H.91 were on order.

Upon the efficiency of the personnel who take over each aircraft when it lands on an aerodrome or touches down on the water depends the reliability of every machine and of every instrument and item of its equipment. The organization of the maintenance facilities along the two trunk routes, one to India and Australia, and the other to South Africa, demands a high standard of reliability.

For the landplanes the headquarters of the service are at Croydon Airport, where one hangar is devoted to overhauls and another to maintenance. The engine shops at Croydon overhaul the engines of landplanes and of the flying boats. The engines of the flying boats are generally carried in lorries to and from Hythe, near Southampton.

The establishment at Hythe is on the western shore of Southampton Water, a short distance by water from Southampton, although the journey by road is circuitous. Hythe bears much the same relation to the flying boats as Southampton Docks to liners, as each flying boat is “turned round” at Hythe, usually within two days. If an extensive overhaul is necessary, requiring a longer stay, the flying boat is towed to the eastern shore of Southampton Water to another establishment of Imperial Airways near Hamble, where she is overhauled. She is then towed back to her mooring off the main establishment at Hythe.

During 1937 and 1938 the substantial increase in the volume of air mail made the activities at Hythe vital to the regular operation of the mail services. Although there are plans for a base at Langstone Harbour (between Hayling Island and Portsmouth), Hythe is the main “dock” at present. On her return from a round voyage the flying boat is moored off the station. Chairs, floor coverings, table linen, lifebelts and other articles are removed for cleaning, inspection and renovation. The weight of the flying boat is thus reduced. The unloaded weight, about 27,000 lb., is indicated by figures painted on the hull of the flying boat.

Skilful manipulation is required for the operation of getting the flying boat from the mooring to the slipway, hauling her out of the water, turning her at a right angle and towing her to the hangar or to her station on the tarmac. The conditions in which the hauling of the flying boat out of the water and launching it again are carried out depend on the weather, tide and other complications. One of the most important of these is the commotion of the water caused by any large vessel proceeding along Southampton Water at the critical moment when the flying boat is about to be hauled up the slipway.

Although high water is the most suitable stage of the tide for beaching or launching, operations are not restricted to high water because of the length of the slipway and the dredging that has been done. During neap tides, when the rise-and-fall of water is at the minimum, operations are possible at almost any stage of the tide except at dead low water. During spring tides, when the rise-and-fall of water is at the maximum, beaching is not undertaken for an hour or so before and after low water. The draught of a laden flying boat is 4 ft. 6 in. and, although that of the unladen aircraft to be beached is less, the maximum draught is allowed for so as to provide a safety margin.

The slipway has no rails. The beaching gear consists of port and starboard legs and a cradle for the stern; legs and cradle are provided with wheels. Haulage power is provided by a power winch or tractor.

The first stage in beaching is to tow the flying boat from her mooring in the stream by a launch to the mooring at the end of the slipway out of the run of the tide. A seaman stands in the mooring compartment and the flying boat is moored by the head. Other seamen of the beaching party proceed to attach the port and starboard adjustable legs, or launching wheels, to the hull and the wings. Each leg consists of a heavy gauge steel tube fitted with two cylindrical floats. In the space between the two cork cylinders are attached two stays, each with a spherical float; the base of the leg is attached to an axle between two pneumatic tyred wheels. The top of the leg is fixed into the fitting provided on the underside of the wing, and the two stays are clamped into the fittings provided in the hull of the flying boat. The leg is balanced by the floats, and should it fall into the water the whole apparatus will not sink below the surface.

When the legs are in position a rope is made fast to the mooring ring in the stern of the hull and the aircraft is pulled round until she is floating in the water over the slipway, in line with the slipway and stern-on to it. A seaman of the beaching crew, wearing waders, walks down the slipway into the water and fastens the stern cradle under the stern to the fittings provided for it. The cradle has two wheels, to the axle of which is attached a shaft. By turning the shaft to right or left, or keeping it straight, the aircraft is steered when she is being hauled up by the tractor.

Salt Water is Washed Off

At this stage the aircraft is waterborne, but is provided with three pairs of wheels so that she will constitute a six-wheeled tricycle when she is hauled up. At a signal from the officer in charge, the tractor begins to travel at right angles to the slipway. The hauling cable passes over pulleys fixed in position to afford a pull in direct line with the slope of the slipway. The cable pulls the flying boat, guided by the seaman at the shaft of the trolley, stern-first out of the water. At the same time the cable from the mooring to the bow of the hull is paid off.

Directly the hull is clear of the water a member of the party directs a stream of fresh water on to the hull, washing off the salt Water and any slime. During the halt made to ensure that every item of the beaching gear is in perfect alinement, an inspector enters the hull and begins his careful scrutiny. A power winch, operating through pulleys, hauls the aircraft to the top of the slipway where the tractor resumes hauling, the steering being done by the seaman at the shaft of the stern cradle.

On a fine day in summer beaching a flying boat appears to an onlooker to be a pleasant occupation; in winter, particularly if the wind is strong, the work is difficult and uncomfortable, especially at night. Even in pleasant conditions the work needs constant care. Lovely as a great liner looks as she moves along the tideway past Hythe, the beaching party is concerned not with her beauty but with her wash.

Near the slipway is a creek which fills at high water; the suction of the Queen Mary as she passes empties this creek — and then the water returns with a rush. Her passage and the subsequent commotion are not frequent and can be anticipated, but during the crucial moments when a flying boat is about to emerge from the water a careful watch is kept on any vessel under way. Speed, in addition to the draught of passing ships, affects the water at the slipway. The officer in charge watches and awaits his opportunity to get the flying boat on to the slipway in calm water so that the weight is evenly distributed between the three sets of wheels.

Wind is another important factor. It would be unsafe to attempt to beach a flying boat in a gale, but impracticable to wait for a dead calm. In practice, beaching and launching are not often prevented by bad weather, owing to the skill and experience of the beaching parties. Prevailing conditions determine the time required for each operation. On one occasion an officer and six seamen beached three flying boats and launched two, a total of five aircraft, in rather more than four hours. It is vitally important to have intimate knowledge of the vagaries of the local tides, and of the various effects that the strength, direction and duration of the wind have on the height of the tide and the waterborne flying boat.

Launching is easier than beaching. It takes longer to transfer the aircraft from water to land than from land to water. When the aircraft is launched she is towed by a launch to her mooring on the station.

The fact that the stern cradle can be turned in any direction enables the flying boat to be pivoted round on her own axis when in the hangar or on the apron. While she is being beached, if the aircraft is slewed out of the desired fore-and-aft direction by a surge of water so that one leg might overrun the edge of the slipway, the craft is eased backwards until she is floating again; the beaching is then begun again. All chance of damage to the flying boat is thus avoided.

Work at Hythe is divided into two shifts. The morning shift begins at 6.15 a.m. and continues until 2.15 p.m. The afternoon shift is from 2.30 to 10.30 p.m. When the flying, boat emerges from the water for her normal period of overhaul, all the adjustments are usually completed within the two days, each of sixteen working hours. She is not dismantled after every round trip but is maintained for the continuance of the Certificate of Airworthiness. Each instrument or part is examined at the requisite interval for certification, but not all the items are examined simultaneously. The flying boat is therefore maintained in service, and it is not necessary to withdraw her for a considerable period.

The four Bristol Pegasus radial air-cooled motors, each with a normal horsepower of 740, are removed for overhaul after 250 hours of operation. The schedule is arranged so that all the four engines do not need removing during the time the aircraft is at Hythe between voyages. Engines to be changed are sent to the main workshops at Croydon and are replaced by others which have been returned in the engine shops. The remaining engines are cleaned.

There are fittings in each engine nacelle to enable the derrick used to lift the engine to be fixed in position, and also to facilitate removal of each De Havilland variable pitch three-bladed airscrew. While this work is in progress other men are at work on the hull. They are immune from splashes of oil from the engines on which work is proceeding above them.

The engine mechanics make use of a staging mounted on trolley wheels. The staging is fitted with a platform with two funnels, below which are pipes leading to receptacles. The mechanics are able to drain the engine oil through one funnel and proceed without letting oil or grease drop below the aircraft. The second funnel is used for depositing dirty and oily rags.


THE ACCESSORIES HAVE TO BE CHECKED as well as the engines, hull and airframe when a flying boat is overhauled The accessories include such items as petrol piping, oil coolers, gauges, coils, batteries, radio and other instruments. The instruments are an important part of the aircraft’s equipment, and this photograph shows an engineer checking over engine instruments as he varies the opening of the throttles.

The airscrews are carefully overhauled at regular intervals, the normal interval being 270 hours of flying. The blades are removed and the hub gear is dismantled, each part being taken to the appropriate unit in the workshops. To detect any crack in the steel parts of the variable pitch gear, an electro-magnetic apparatus is used. An electro-magnet magnetizes the part under examination, over which a solution of iron filings and paraffin is poured. If there is a fracture the filings form in a small heap across the gap and reveal it. The surface of each of the blades of the propellers is examined through a magnifying glass for scratches, and any mark is indicated for the scrutiny of the inspector. When the airscrew has been renovated, and before it is replaced, it is tested on the balancing apparatus to ensure that the balance is still true.

When the inspector boards the aircraft as she is being hauled out of the water, he compiles a list of the jobs to be done. The sheets are passed to the man in charge of each section and the work is put in hand. After completion the job is inspected and passed.

To avoid risk of corrosion, every square inch of the hull, floats and wings is subjected to a close scrutiny to ensure that there is no dent or scratch that has removed the protective covering of the metal. The wing-tip floats amply protect the hull from the rubbing of small craft, and dented floats are easily repaired or replaced. Occasionally, however, small pieces of floating debris may come into contact with the hull of the flying boat when it is on the water. At times baulks of timber and other obstacles dangerous to the hull of a flying boat are seen being carried by the tide towards a moored aircraft, and are retrieved and towed out of the way.

Ailerons, flaps, petrol piping, oil coolers, gauges, coils, batteries, radio and other instruments, and a variety of further items of equipment are dealt with. The flying boat spends part of the time inside the hangar, while some men work on, in and below her, and others are busy in the departments and at the benches arranged on three sides of the hangar. For the ground testing of the engines the flying boat is pulled out of the hangar on to the tarmac. Marked on the concrete are the compass points (north, north-east, east, south-east, south, south-west, west and north-west), so that the flying boat can be turned with her head on any one of these points to enable the compass to be checked.

After the flying boat has been launched bags of ballast are placed on board to bring the load to the maximum, representing a full complement of passengers and mail, and the test flight is made.

In June 1938 the schedule of departures and arrivals was as follows:


Sunday, one departure East (India or beyond)

Monday and Tuesday, none

Wednesday, one East and one South (South Africa)

Thursday, one East

Friday, one East and one South

Saturday, one South.


Sunday, one West (from India or beyond)

Monday, one West and one North (from South Africa)

Tuesday, one North

Wednesday, none

Thursday, one West

Friday, one West and one North

Saturday, none.

There are facilities for repairs at all airports on the two routes, but the major airports are more elaborately equipped than the others. Those at Alexandria, Egypt, where the two trunk routes diverge, are extensive. On the Eastern route the key airports are Karachi, Calcutta and Singapore. Beyond Singapore the route is operated by the Qantas aircraft. On the Southern route the key bases are at Kisumu, Kenya and Durban.

A flying boat leaving Hythe on either route may or may not proceed all the way either to Singapore or to Durban. She may be turned at any airport in accordance with traffic requirements.

Sea-Anchors are Sometimes Used

The sea-anchor is used-in some conditions of wind and tide to enable a flying boat to swing to the tide, so that she does not yaw about under the influence of wind conflicting with the tide.

At Croydon work in the maintenance hangar goes on throughout the twenty-four hours. There are three shifts, from 6 a.m. to 2 p.m., from 2 to 10 p.m., and from 10 p.m. to 6 a.m. Every member of the staffs at each establishment is an expert in his particular sphere. From time to time members are attached to the various establishments where the aircraft, engines, instruments and accessories are manufactured. The object of this is to enable the staff to keep in touch with the latest developments. An item which requires the attention of the manufacturers is sent to them for inspection, and repair if this proves necessary.

The excellence of the British craftsmanship in every detail of the landplanes and the flying boats has simplified the work of maintenance. As each component of a new aircraft is attuned in service on the routes to the machine, and the idiosyncrasies of the individual component are noticed in flight, logged and corrected by the maintenance department, the length of time between each overhaul is extended progressively. The airscrews of the flying boats began service with overhauls after 100 hours; the interval has now increased to 270 hours. The De Havilland Gipsy engines of some of the air liners now run for 600 hours between overhauls.

After the preliminary flights the aircraft is attuned to the harmony which makes her an instrument in the hands of the pilot. Although it seems but yesterday that the Canopus was the newest aircraft in the world, she is relatively old. Seeing her emerge from the water to be groomed at Hythe, the onlooker feels that sentimental regard which is the right and proper due of a proved ship.

ON THE RETURN TO HYTHE after a round voyage, chairs, floor coverings, table linen, lifebelts and other articles are removed from the flying boat

ON THE RETURN TO HYTHE after a round voyage, chairs, floor coverings, table linen, lifebelts and other articles are removed from the flying boat for inspection and renovation. The removal of these items lightens the aircraft and thus makes the task of hauling it up the slipway easier. The unladen weight of one of the Empire flying boats is about 27,000 lb.

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You can read more on “Aircraft Electrical Equipment”, “Certificate of Airworthiness” and “Short Brothers” on this website.

Aircraft Maintenance