First of all, there is an ice detector probe located on the fuselage nose (left side). The probe expands and contracts at 40,000 Hz - so fast that nothing but ice can cling to it. A build-up of ice will slow down the probe and two things happen. It turns on an amber ICING light on the pilot's caution and warning panel, and it turns on a probe heater to melt the ice. The heater Is "on" for 5 seconds. The ICING light is on for 60 seconds, then will turn off if the condition were momentary, but would remain "on" if the icing condition is continuous.
Turning "on" the light on the ground can be simulated by wearing a pair of gloves and gripping the probe sufficiently to have the ICING light illuminate. It is important to be wearing gloves, because the probe heater is also turned on.
The ICING light being on for more than a minute is a "signal" to the flight crew to turn on the anti-ice systems.
The Wing Anti-Ice panel is on the Pilots' Overhead Panel. I have already discussed the two DUCT FAIL lights on the panel - they are a part of the Pneumatic system Area Overheat System.. The left and the right systems of wing anti-ice are identical. For either side there are two modes of operation - automatic (through a controller) and manual (direct signal to the valve). The ON light is simply switchlight position. When the pressure-regulating shutoff valve (PRSOV) is open, the OPEN light will illuminate in the MANUAL switchlight - regardless of which system is in operation. The signal to illuminate the OPEN light is controlled by a pressure switch immediately downstream of the valve. Supply of hot air is the method of anti-icing. When the AUTO switchlight is latched in, the controller will cause the valve to cycle open/closed/open - to maintain slat skin temperature between 105°C at the high end and 50°C at the low end. Only the four outboard slats - #4, 5, 6, 7 - are heated (the slats outboard of the engine pylon). If slat #4 temperature reaches about 120°C, the OVHT light in the AUTO switchlight will illuminate - indicating that the controller did not close the PRSOV when it should have. The pilots would then have to unlatch the AUTO switchlight.
If there is a problem with the anti-ice controller, the wing anti-ice system can be operated in the Manual mode, by latching in the MANUAL switchlight. The ON light in the Manual switchlight will illuminate (switchlight position). The OPEN light in the same switchlight will illuminate when the PRSOV opens and pressure is supplied. In the Manual mode, control is only via switchlight (no controller), so when the OVHT light in the AUTO switchlight illuminates, then a pilot would unlatch the respective MANUAL switchlight to close the PRSOV and wait for the OVHT light to extinguish. At the same time (in either mode of operation) signals are sent to the pneumatic system to supply hotter high pressure air.
So for all four switchlights, the upper ON legend indicates switchlight position and the lower half of the switchlights in either the left or right system indicate situations relating to that half - regardless of mode of operation. And, it is possible to have the left side in AUTO and the right side in MANUAL.
The system normally functions only in flight, assuring sufficient airflow over the slats to dissipate the very high temperatures that are created by the hot anti-icing air. To test the systems on the ground, latch in one switchlight per side and press and hold the TEST switch. The valves will open (OPEN lights). Note: Be certain to release the Test switch immediately if an OVHT light illuminates.
For Engine Inlet Anti-Ice, intermediate pressure bleed air from the given engine is used. The Engine Anti-ice panel is located on the Pilots' Overhead Panel, The white ON light indicates that the switchlight is latched in. The green HEAT light indicates that the PRSOV is open and pressure in the duct is at least 5 psi. If pressure exceeds 40 psi (engines 1 and 3) or 26 psi (engine 2), the amber
HI PR (high pressure) light will illuminate. There is no need for the flight crew to react, since a mechanically operated pneumatic relief valve will open to allow the excess pressure to be relieved overboard. The reason the high pressure setting is so much lower for engine #2 is that there is a very long duct from the PRSOV to the S-duct inlet for engine #2, and it is expected that there will be a significant pressure drop from the PRSOV to the engine inlet.
Some of the warm air for engine inlet anti-icing is also used to heat the P1 probe for the respective engine. For engines 1 and 3, the P1 probe in is the nose cowl. For engine #2, the P1 probe is about half way up/down the S-duct.
The was also a VHF anti-ice system, using hot air from from the #2 and #2 pack supply ducting, functioning only when engine #2 anti-ice had been selected ON. The air was supplied via two motor-operated shutoff valves located in the right-hand ECS Compartment, with air conditioning packs #2 and #3. However this system has been deactivated on L-1011s on which it had been installed, and is deleted on newer production. I don't have the s/n when this change was incorporated. It was originally thought, later proven wrong, that an ice build-up on the upper VHF antenna could find its way into the #2 engine inlet. There were no separate controls for this system. Its operation was "automatic".
Don
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