The
RAM
AIR DUCT system supplies and controls cooling air to the air-to-air
heat exchangers of the air condition packs. As the word describes it uses ram
air created by forward motion of the aircraft. On the ground airflow is created
by a fan which is turned by the AIR CYCLE MACHINE (ACM).
On
the ground, a DEFLECTOR DOOR mounted at the inlet of the duct extends to
prevent debris from entering the duct when taking off or landing on a
contaminated runway. The nose wheels spurt
contamination sideways and up in the direction of the ducts where it becomes
deflected away from them, to minimize clogging the air-to-air heat exchangers
inside the ducts. When the heat exchangers clog up, it might affect temperature
control of the PACK possibly creating an overheat and a PACK tripping of.
Inside
the duct are the RAM AIR DOORS (RAM AIR MODULATION PANELS) mounted that modulate
to accomplish a constant temperature of 110°C measured between the ACM
compressor and the secondary air-to-air heat exchanger. As most of the air
condition components this is measured and controlled by the AIR
CONDITION ACCESSORY UNIT (ACAU) in conjunction with the PACK/ZONE
CONTROLLER.
On ground;
The ACAU commands the RAM AIR DOORS to be completely open indicated by the RAM DOOR FULL OPEN light(s) to establish the best cooling flow with slower, or no forward motion of the aircraft.
The ACAU commands the RAM AIR DOORS to be completely open indicated by the RAM DOOR FULL OPEN light(s) to establish the best cooling flow with slower, or no forward motion of the aircraft.
In flight:
The ACAU commands the RAM AIR DOORS to move from the open position, modulating to such a position to maintain that 110°C duct temperature, mainly at a faired position to reduce drag. The FCOM states that the doors will be fully open indicating the RAM DOOR FULL OPEN in slow flight with the flaps not fully UP. This is a result of low airflow causing the air temperature to reach the 110°C not being able to maintain a lower temperature which drives the door to full open. In the ACAU and PSCU (AIR/GND) systems that control the doors are no speed reference signal inputs.
The ACAU commands the RAM AIR DOORS to move from the open position, modulating to such a position to maintain that 110°C duct temperature, mainly at a faired position to reduce drag. The FCOM states that the doors will be fully open indicating the RAM DOOR FULL OPEN in slow flight with the flaps not fully UP. This is a result of low airflow causing the air temperature to reach the 110°C not being able to maintain a lower temperature which drives the door to full open. In the ACAU and PSCU (AIR/GND) systems that control the doors are no speed reference signal inputs.
Other possibilities
of an illuminated RAM DOOR FULL OPEN indication but with flaps UP,
even at cruise altitudes could be:
- The ram air duct could have an obstruction
- One or both air to air heat exchangers are dirty not allowing enough airflow through them
- An electrical failure causing a high temperature sensing or door fails in open position.
- The ram air duct could have an obstruction
- One or both air to air heat exchangers are dirty not allowing enough airflow through them
- An electrical failure causing a high temperature sensing or door fails in open position.
