Anti-Ice External Air Duct The anti-ice external air duct is connected to the inlet of the anti-icing valve and to the 14th stage of the engine to provide hot 14th stage bleed air to the anti-icing system. Forward  Anti-Ice  Duct The forward anti-ice duct is connected to the engine nose pylon and the air inlet fairing anti- ice duct to provide hot 14th stage bleed air to the air inlet fairing. BLEED-AIR  LEAK  DETECTION The S-3 aircraft bleed-air leak detection system consists of four loops of bleed-air leak sensing elements located close to the auxiliary power unit (APU) duct, bleed-air ducts, and an engine start port leak detector located near the engine ground start port. Sensing elements are mounted between ducts and the aircraft structure because bleed-air temperature is sufficiently high to cause structural damage.   Support   clamps   with   quick-release fasteners are used to mount the sensing elements, which are protected by bushings. The bleed-air leak  detector  control  is  located  in  the  lower section of the left load center. This system is a fire-detection type of system that responds to heat. High temperature causes a chemical reaction in the sensing element, which provides a ground for the warning circuit and turns on an indicator light on   the   annunciator   panel.   A   test   circuit is activated by the bleed-air leak detect switch on   the   eject   panel   located   on   the   eyebrow panel. The bleed-air leak detection system is powered by single-phase, 400-Hz, 115-Vac power from the essential ac bus. The test circuit uses 28 Vdc from the essential dc bus. When the bleed-air leak detect switch  on  the  elect  panel  is  held  in  the  TEST position, 28 Vdc is applied to the test relays. This completes  the  transformer  circuit  through  the sensing  elements  to  ground.  The  transformer conducts  and  applies  a  signal  to  a  transistor circuit,  which  closes  control  relays.  A  ground circuit  is  completed  through  the  control  relay contacts to turn on the 1 BL LEAK, 2 BL LEAK, CAB LB LEAK, and APU BL LEAK indicator lights   on   the   annunciator   panel.   When   the momentary bleed-air leak detect switch is released 1-18 to   the   OFF   position,   the   annunciator   panel indicator lights go off. In normal operation, when the temperature of a section or a short segment of the sensing element exceeds 255°F (107°C), the chemical in the tube conducts electric current, which  completes  a  transformer  circuit  to  ground similar to the test relay. The indicator light on the annunciator panel will come on to indicate the loop  that  is  overheating.  This  system  will function even if there is an open (break) in the loop. During test position, the open element will prevent the indicator light from turning on. The individual   loops   will   function   separately   or simultaneously  if  a  leak  is  located  in  an  area common to two loops. This will allow the pilot to take action to minimize damage due to bleed- air  leakage. The  bleed-air  leak  detection  system  consists of a bleed-air leak detector control, bleed-air leak sensing elements, and an engine start port leak detector. Bleed-Air  Leak  Detector  Control The detector control is located in the lower section  of  the  left  load  center.  The  detector control contains two modules with four electrical circuits. Each circuit has a test function and a control  function.  The  test  function  verifies  all sensing element loops, and the control function turns   on   a   warning   indicator   light   on   the annunciator panel. Bleed-Air Leak Sensing Elements The sensing elements are metal tubes with center conductors isolated from the tubes by a solid chemical. The sensing elements are mounted between  the  bleed-air  ducts  and  areas  to  be protected from very high temperatures that would develop if a duct were punctured or ruptured. The sensing elements are mounted within 2 to 5 inches of the duct. Engine Start Port Leak Detector The  leak  detector  is  mounted  inside  the  right main landing gear door. The leak detector is a heat-sensitive element that completes a ground circuit  when  subjected  to  temperatures  in  excess of 255°F (107°C). Its purpose is to detect leakage from the engine ground start port in the event of