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BOEING 727 RAIN & ICE PROTECTION

 

Engine and Wing Anti-Ice...

The Boeing 727 uses engine bleed air for engine and wing anti-ice protection. Each engine provides its own bleed air for its respective cowl and inlet anti-icing capabilities, while engines 1 and 3 provide bleed air for the wing anti-ice system.  After the bleed air passes through the wing venting, it is exhausted through vents in the area of the wing tip.Typically, both bleed sources are used in icing conditions.

Anti-ice should never be used with outside temperatures exceeding 10 C. As the bleed air is extremely hot, the excess heat will soften the engine cowl and wing leading edge. Should a valve stick open, the thrust on the associated engine should not exceed 80% N1 RPM and be kept as low as possible. (Softening of the cowl and leading edge of the wing reduces the hail resistance of those surfaces.)

Should one of the wing anti-ice valves not open in icing conditions, the engine supplying air to the system should be run at a minimum of 75% N1 RPM to ensure adequate anti-icing capabilities.

Indications of ice build up include accumulation of the windshield wipers (visible to the pilots) and possibly erratic EPR readings in the case of engine icing.

Pitot Heat...

Cockpit switches for pitot heat control the electrical heating of pitot tubes, static ports, and the temperature probe. Pitot heat should be on before takeoff and should remain on until after touchdown.

Windows and Window Heat...

All cockpit windows on the Boeing 727 consist of two panes of glass, with the structural integrity of the inner pane. Should an inner pane crack, heat to that window must be removed and the maximum pressure differential reduced to 5 PSID. If both panes crack, window heat must be turned off and the pressure must not exceed 2 PSID. Cabin altitude should not exceed 10,000 feet under these circumstances. With a 2 PSID, maximum altitude at which a 10,000-foot cabin altitude can be maintained is about 15,000 feet. (5 PSID with a 10,000-foot cabin is about 25,000 feet.) There are no restrictions if just the outer pane cracks.

Window heat both defogs and anti-ices the windows. It also makes the window more resistant to impact (from birds, etc.). Window heat should be on from preflight through shutdown. Should window heat be turned off in flight, the aircraft should not exceed 250 knots below 10,000 feet or any other time there is the possibility of a bird strike.

Rain Removal...

The windshield wipers on the 727 are the main means of removing rain from the windshields. During periods of heavy rain, windshield rain repellent can be used in conjunction with the windshield wipers to improve visibility. The repellent should not be applied to dry windshield. Should the repellent be accidentally applied to a dry windshield, the wipers should not be used to remove it.