17.7 Propeller Storage and Preservation

Question 1

The preservation and de-preservation procedures and storage periods for both serviceable and unserviceable installed propellers are found in the Aircraft Maintenance Manual (AMM)

Answer 1

while uninstalled propeller preservation, depreservation procedures and storage periods are found in the Propeller Maintenance Manual (PMM).

Question 2

Storage periods for propellers are typically divided up into periods of up to:

Answer 2

3 months - short-term
6 months - long-term
12 months - long-term
3 years - long-term

Question 3

Installed Propellers
periods up to 3 months

Answer 3

installed wooden propellers must be kept in a clean condition and inspected at regular intervals.

Question 4

(Periods up to 3 Months)

Wooden fixed pitch propellers must be placed in a horizontal position to ensure that there is even moisture distribution. They must be cleaned with a mild solution of soap and water and inspected for damage.

Answer 4

The blades must be adequately ventilated and, if possible, the storage area must be clean, warm, dry, dark and well ventilated as well as free from corrosive vapours. Ideal storage temperatures are between 10°C (50°F) and 20°C (68°F).

To prevent rot, wooden propellers should not be wrapped in any way that would seal it off from the air.

Question 5

(Periods up to 3 Months)

The procedure for metal fixed pitch propellers is similar to wooden but with the addition of regular corrosion inspections.

Answer 5

.

Question 6

(Periods up to 3 Months)

Variable pitch propeller pitch change mechanisms need to be exercised to circulate the oil in the pitch change mechanism prior to engine shut down. On completion of the ground run, the propeller must be cleaned using a mild solution of soap and clean water and inspected for signs of corrosion.

Answer 6

.

Question 7

Periods up to 6 Months

If the propeller is to be stored on the wing for periods in excess of 3 months then what must happen

Answer 7

the pitch change mechanism must be flushed using an inhibiting oil and then covered with waxed paper.

All external parts must be treated with lanolin or an approved anti-corrosive treatment and inspected regularly for corrosion

Question 8

Ensure that lanolin does not come into contact with the de-icer boots

Answer 8

.

Question 9

Preservation of Uninstalled, Assembled Propellers

(Short-term Storage up to Three Months)

Answer 9

If a wooden propeller has an automatic pitch change mechanism, the hub must be filled with oil. The propeller must be turned every two weeks to ensure that the internal surfaces of the hub are coated with oil. Regular inspections must be made for signs of deterioration

Question 10

Variable pitch propellers must have been exercised prior to their removal. If they remain assembled, they must be cleaned and then stored in a warm, dry and dust free environment, free from corrosive vapours. Ideal storage temperatures are between 10°C (50°F) and 20°C (68°F).

Answer 10

.

Question 11

Propellers with metal blades must be stored in an upright position on stands where the hub is supported by what

Answer 11

a mandrel

Question 12

The external surfaces of the propeller must be coated with lanolin or an approved corrosion inhibitor.

Answer 12

.

Question 13

The pitch change mechanism must be drained of oil and flushed with approved inhibiting oil. The pitch change mechanism surface must be coated in lanolin and the mechanism must be wrapped in waxed paper.

Answer 13

.

Question 14

The oil transfer tubes and the propeller attachment parts must be cleaned, coated in lanolin and wrapped in waxed paper.

Answer 14

.

Question 15

All parts used to secure the propeller to the engine, including the oil transfer tubes, retaining nut assemblies and the location cones are considered to be propeller parts and must accompany it both into storage and while in transit.

Answer 15

.

Question 16

Long-term Storage up to Six Months

The procedure for wooden propellers remains the same as for short-term storage up to three months

Answer 16

.

Question 17

Long-term Storage up to Six Months

For metal, variable pitch propellers the procedure is the same as for short-term storage up to three months, with one exception:

Answer 17

If the propeller blades have pre-loaded bearings, the blades must be rotated to prevent the bearings from brinelling. This must be carried out at the six months point.

The rotation procedure is carried out by marking the blade positions relative to their bearings prior to rotating each blade with an approved turning paddle. The blade is turned through its full range of travel at least three times

If the check is satisfactory, the blade must be left at a position at least one inch away from its original position.

Question 18

Long-term Storage up to Twelve Months

The storage procedures remains the same as for the three and six month examples except that, for pre-loaded blades

Answer 18

the blades require exercising after six months and nine months. At twelve months, the bearings must be removed and visually examined for signs of ‘brinelling’ and corrosion. If satisfactory, the bearings must be cleaned, greased and reassembled on to the blades. The propeller must then be re-inhibited and re-protected.

Question 19

Long-term Storage over Twelve Months

Answer 19

The storage procedure remains similar to that of the three, six and twelve month examples

However, each year, the blades require exercising at the six months and the nine months stage, followed by bearing removal and inspection at the twelve months point.

The propeller requires re-inhibiting at each twelve months point. At the three year stage the propeller must be sent for overhaul. The overhaul includes a hub/blade inspection as required by AWN75.

Question 20

Long-term Preservation of Uninstalled, Dismantled

Long-term Storage up to Six Months, Twelve Months and Three Years (Uninstalled and Dismantled)

Answer 20

If the propeller is dismantled and remains in its original manufacturers’ packing it does not require re-inhibiting every twelve months

However, if the blade bearings are in a pre-loaded condition, they are still subject to the requirement for exercising at the six month and nine month periods each year and the annual dismantling and inspection procedure.

Providing these requirements are met, the propeller can remain in storage for up to three years, at which time it must be returned for overhaul.

Question 21

All the propeller parts must be wrapped in waxed paper and packed into an approved crate. The crate must be labelled with

Answer 21

The propeller type and serial number
Component part numbers
The modification standard
Original date of preservation
The dates of the blade bearing exercise and inspections if applicable

Question 22

Providing the propeller remains in its packing, it can remain in storage for up to three years prior to being overhauled

Answer 22

.

Question 23

All parts held in storage require the appropriate Form 1 - Certificate of Conformity (COC), and a valid Certificate of Release to Service (CRS).

Answer 23

.