104 had problems with ice formation on upper wing surfaces, even at above-freezing temperatures, due to the presence of cold fuel in the wet wings. (“Wet wings” refers to integral wing fuel tanks. See “Fuel Systems” in Chapter 5.) Fuel lines were rerouted in that design to address the problem, and electrically heated thermal panels were developed for ground heating of its upper wing surfaces.
Rain Protection In addition to icing liabilities, turbine engines are also vulnerable to flameout (engine failure due to smothered combustion) if large amounts of water are ingested in flight. In precipitation this problem is addressed by selecting “igniters on” and in some cases operating at higher power settings. Many turbine aircraft also have windshield rain protection systems, for purposes of preserving visibility on takeoff and landing. Along with heavyduty windshield wipers, many larger jets use rain repellent chemicals, which may be released onto the windshield from the cockpit. Rain repellent chemicals reduce adherence of water to the windshield by changing its viscosity and slipperiness. The result is reduced formation of water droplets on the windshield and, therefore, enhanced visibility. Neither wipers nor rain repellent fluid should ever be used on a dry windshield!
Automatic Ice Protection Systems Newer aircraft designs incorporate fully automatic systems for ice protection. These systems use ice detectors to identify icing conditions and when appropriate, automatically alert engine bleed-air management controllers to activate wing and enginecowl anti-ice systems. These systems will continue to operate automatically until the ice detectors no longer detect any icing. Amazingly, most systems will also recognize engine-out situations or other relevant system failures, and configure all valves appropriately to ensure sufficient heat for anti-icing. Traditional manual deice and anti-icing systems require a good deal of pilot attention for proper operation, so these new automated systems greatly reduce cockpit workload.
THE TURBINE PILOT’S FLIGHT MANUAL
Landing Gear Systems While there are a few fixed gear models around (such as the DHC-6 Twin Otter and the singleengine Cessna Caravan), retractable landing gear is found on most turbine aircraft. Some older airplanes used electrically powered, gear-driven landing gear retraction systems. These proved to be heavy and electrically demanding, with high maintenance requirements due to the large forces required to extend and retract landing gear. Hydraulic power has proven to be ideal for this purpose and is found on virtually all of today’s retractable landing gear systems. Light turbine aircraft, such as the smaller King Airs, often use the same types of electrically powered hydraulic power packs found in general aviation piston aircraft. On these systems, an electric motor drives a dedicated hydraulic pump, based on pilot selection of the gear handle. Hydraulic lines transmit the generated hydraulic pressure to power landing gear operation. Most large aircraft have generalized, multipurpose hydraulic systems, of which one major duty is powering landing gear operation. Gear doors on these systems are usually also hydraulically powered through the use of piston-type hydraulic actuators. Door operation may be separately controlled or may be made part of the gear retraction cycle through the use of hydraulic sequencing valves in the landing gear hydraulic circuit. On some aircraft, gear doors are linked mechanically to landing gear operation, using some combination of pushrods, cables, or pins. All aircraft having retractable gear are required to have pilot warning systems in order to reduce the likelihood of unintentional gear-up landings. In most cases, gear warning horns are designed to sound when the landing gear is retracted, and some combination of flap position, low power setting, and perhaps airspeed suggests imminent landing. You’ll be required to memorize the gear warning conditions for aircraft you fly. Other safety features are built into landing gear systems to confirm proper position and operation of the gear. Sensors known as landing gear position switches are located at every landing gear strut to confirm gear position as up and locked or down and locked, as appropriate. These are usually
