Aircraft Wing and Stabilizer Deice Boots Maintenance and Troubleshooting

Construction and Installation of Deice Boots

Deicer boots are made of soft, pliable rubber, or rubberized fabric, and contain tubular air cells. The outer ply of the deicer boot is of conductive neoprene to provide resistance to deterioration by the elements and many chemicals. The neoprene also provides a conductive surface to dissipate static electricity charges. These charges, if allowed to accumulate, would eventually discharge through the boot to the metal skin beneath, causing static interference with the radio equipment. [Figure 1]

Figure 1. Deicing boots inflated (left) and deflated (right)

On modern aircraft, the deicer boots are bonded with an adhesive to the leading edge of wing and tail surfaces. The trailing edges of this type boot are tapered to provide a smooth airfoil. Elimination of fairing strips, screws, and rivnuts used on older types of deicing boots reduces the weight of the deice system. The deicer boot air cells are connected to system pressure and vacuum lines by non-kinking flexible hose.

When gluing the deice boots to the leading edge of wings and stabilizers, the manufacturer’s instruction must be strictly followed. The glue is typically a contact cement normally spread on both the airfoil and the boot and allowed to become tacky before mating the surfaces. Clean, paint-free surfaces are required for the glue to adhere properly. Removal of old boots is performed by re-softening the cement with solvent.

Inspection, Maintenance, and Troubleshooting of Rubber Deicer Boot Systems

Maintenance on pneumatic deicing systems varies with each aircraft model. The instructions of the airframe or system components manufacturer should be followed in all cases. Depending on the aircraft, maintenance usually consists of operational checks, adjustments, troubleshooting, and inspection.

Operational Checks

An operational check of the system can be made by operating the aircraft engines or by using an external source of air. Most systems are designed with a test plug to permit ground checking the system without operating the engines. When using an external air source, make certain that the air pressure does not exceed the test pressure established for the system. Before turning the deicing system on, observe the vacuumoperated instruments. If any of the gauges begin to operate, it is an indication that one or more check valves have failed to close and that reverse flow through the instruments is occurring. Correct the difficulty before continuing the test. If no movement of the instrument pointers occurs, turn on the deicing system. With the deicer system controls in their proper positions, check the suction and pressure gauges for proper indications. The pressure gauge fluctuates as the deicer tubes inflate and deflate. A relatively steady reading should be maintained on the vacuum gauge. It should be noted that not all systems use a vacuum gauge. If the operating pressure and vacuum are satisfactory, observe the deicers for actuation. With an observer stationed outside the aircraft, check the inflation sequence to be certain that it agrees with the sequence indicated in the aircraft maintenance manual. Check the timing of the system through several complete cycles. If the cycle time varies more than is allowable, determine the difficulty and correct it. Inflation of the deicers must be rapid to provide efficient deicing. Deflation of the boot being observed should be completed before the next inflation cycle. [Figure 2]

Figure 2. Test equipment used to test a wing deice system (left), and test equipment installed in the aircraft for testing (right)

Adjustments

Examples of adjustments that may be required include adjusting the deicing system control cable linkages, adjusting system pressure relief valves, and deicing system vacuum (suction) relief valves. A pressure relief valve acts as a safety device to relieve excess pressure in the event of regulator valve failure. To adjust this valve, operate the aircraft engines and adjust a screw on the valve until the deicing pressure gauge indicates the specified pressure at which the valve should relieve. Vacuum relief valves are installed in a system that uses a vacuum pump to maintain constant suction during varying vacuum pump speeds. To adjust a vacuum relief valve, operate the engines. While watching the vacuum (suction) gauge, an assistant should adjust the suction relief valve adjusting screw to obtain the correct suction specified for the system.

Troubleshooting

Not all troubles that occur in a deicer system can be corrected by adjusting system components. Some troubles must be corrected by repair or replacement of system components or by tightening loose connections. Several troubles common to pneumatic deicing systems are shown in the left-hand column of the chart in Figure 3. Note the probable causes and the remedy of each trouble listed in the chart. In addition to using troubleshooting charts, operational checks are sometimes necessary to determine the possible cause of trouble.

Problem	Causes (most of which can be identified with a 343 Test Kit)	Corrective Action(s)
Boots do not inflate	Open circuit breaker	Reset circuit breaker
	Faulty deflate valve Solenoid inoperable: Improper voltage at solenoid Blocked air vent in solenoid Inoperative plunger Diaphragm not seated Blocked vent orifice located in rivet bottom at center of diaphragm Dirty diaphragm seal area Diaphragm ruptured	Check deflate valves as follows Solenoid inoperable: Correct electrical system Clean with alcohol or replace Clean with alcohol or replace Diaphragm not seated Clean with .010 diameter wire and alcohol Clean with blunt instrument and alcohol Replace valve
	Two faulty deice control valves of faulty two-stage regulators	Clean or replace valve assembly as noted above
	Faulty check valve	Replace check valve
	Relay not functioning	Check wiring or replace relay
	Leak in system boots	Repair as needed
inflateSlow boot inflation	Lines blocked or disconnected	Check and replace lines
	Low air pump capacity	Replace air pump
	One or more deice control valves not functioning properly	Clean or replace valve assembly as noted above
	Deflate valve not fully closed	Clean or replace valve assembly as noted above
	Ball check in deflate valve inoperative	Clean check valve or replace deflate valve
	Leaks in system or boots	Repair as needed
System will not cycle	Pressure in system not reaching specified psi to activate pressure switch	Clean or replace deice control valve as noted above Clean or replace deflate valve, as noted above
	Leak in system or boots	Repair as needed, tighten all hose connections
	Pressure switch on deflate valve in	Replace switch
Slow deflation	Low vacuum	Repair as needed
Slow deflation	Faulty deflate valve (indicated by temporary reduction in suction gauge reading)	Clean or replace valve assembly as noted above
No vacuum for boot hold down	Malfunctioning deflate valve or deice valve	Clean or replace valve assembly as noted above
No vacuum for boot hold down	Leak in system or boots	Repair as needed
Boots will not deflate during cycle	Faulty deflate valve	Check and replace valve
Boots appear to inflate on aircraft climb	Vacuum source for boot holddown inoperative	Check operation of ball check in deflate valve
Boots appear to inflate on aircraft climb	Lines running through pressurized cabin loose or disconnected	Check for loose or disconnected vacuum lines and repair

Figure 3. Troubleshooting guide for wing deice system

Inspection

During each preflight and scheduled inspection, check the deicer boots for cuts, tears, deterioration, punctures, and security; during periodic inspections, go a little further and check deicer components and lines for cracks. If weather cracking of rubber is noted, apply a coating of conductive cement. The cement, in addition to sealing the boots against weather, dissipates static electricity so that it does not puncture the boots by arcing to the metal surfaces.

Deice Boot Maintenance

The life of the deicers can be greatly extended by storing them when they are not needed and by observing these rules when they are in service:

Do not drag gasoline hoses over the deicers.
Keep deicers free of gasoline, oil, grease, dirt, and other deteriorating substances.
Do not lay tools on or lean maintenance equipment against the deicers.
Promptly repair or resurface the deicers when abrasion or deterioration is noted.
Wrap deice boots in paper or canvas when storing.

Thus far, preventive maintenance has been discussed. The actual work on the deicers consists of cleaning, resurfacing, and repairing. Cleaning should ordinarily be done at the same time the aircraft is washed, using a mild soap and water solution. Grease and oil can be removed with a cleaning agent, such as naptha, followed by soap and water scrubbing. Whenever the degree of wear is such that it indicates that the electrical conductivity of the deicer surface has been destroyed, it may be necessary to resurface the deicer. The resurfacing substance is a black, conductive neoprene cement. Prior to applying the resurfacing material, the deicer must be cleaned thoroughly and the surface roughened. Cold patch repairs can be made on a damaged deicer. The deicer must be relieved of its installed tension before applying the patch. The area to be patched must be clean and buffed to roughen the surface slightly. Patches are glued in place. Follow manufacturer’s instructions for all repairs.

Electric Deice Boots

A few modern aircraft are equipped with electric deice boots on wing sections or on the horizontal stabilizer. These boots contain electric heating elements which are bonded to the leading edges similarly to pneumatic deice boots. When activated, the boots heat up and melt the ice off of leading edge surfaces. The elements are controlled by a sequence timer in a deice controller. Ice detector and ram air temperature probe inputs initiate operation when other flight condition parameters exist. The boot elements turn ON and OFF in paired sections to avoid aerodynamic imbalance. The system is inoperative while the aircraft is on the ground. Figure 4 illustrated such a system. A benefit of electric deice boots is the conservation of engine bleed air. Current draw is limited to only those periods when de-ice is required.

Figure 4. Electric stabilizer deice system

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