DUAL BLEED Light
The DUAL BLEED light illuminates whenever the APU bleed air valve is open
and the position of the engine bleed air switches and isolation valve would permit
possible backpressure of the APU. Therefore, thrust must be limited to idle with
the DUAL BLEED light illuminated.
Air Conditioning Packs
The flow of bleed air from the main bleed air duct through each air conditioning
pack is controlled by the respective pack valve. Normally the left pack uses bleed
air from engine No. 1 and the right pack uses bleed air from engine No. 2. A single
pack is capable of maintaining pressurization and acceptable temperatures
throughout the airplane up to the maximum certified ceiling.
The APU is capable of supplying bleed air for two packs on the ground, or one
pack in flight. Most external air carts are capable of supplying adequate bleed air
for two pack operation. Do not operate more than one pack from one engine at
any time.
Airflow Control
With both air conditioning pack switches in AUTO and both packs operating, the
packs provide “normal air flow”. However, with one pack not operating, the other
pack automatically switches to “high air flow” in order to maintain the necessary
ventilation rate. This automatic switching is inhibited when the airplane is on the
ground, or inflight with the flaps extended, to insure adequate engine power for
single engine operation. Automatic switching to “high air flow” occurs if both
engine bleed air switches are OFF and the APU bleed air switch is ON, regardless
of flap position, air/ground status or number of packs operating.
With the air conditioning pack switch in HIGH, the pack provides “high air flow”.
Additionally, an “APU high air flow” rate is available when the airplane is on the
ground, the APU bleed air switch is ON and either or both pack switches are
positioned to HIGH. This mode is designed to provide the maximum airflow when
the APU is the only source of bleed air.
The DUAL BLEED light illuminates whenever the APU bleed air valve is open
and the position of the engine bleed air switches and isolation valve would permit
possible backpressure of the APU. Therefore, thrust must be limited to idle with
the DUAL BLEED light illuminated.
Air Conditioning Packs
The flow of bleed air from the main bleed air duct through each air conditioning
pack is controlled by the respective pack valve. Normally the left pack uses bleed
air from engine No. 1 and the right pack uses bleed air from engine No. 2. A single
pack is capable of maintaining pressurization and acceptable temperatures
throughout the airplane up to the maximum certified ceiling.
The APU is capable of supplying bleed air for two packs on the ground, or one
pack in flight. Most external air carts are capable of supplying adequate bleed air
for two pack operation. Do not operate more than one pack from one engine at
any time.
Airflow Control
With both air conditioning pack switches in AUTO and both packs operating, the
packs provide “normal air flow”. However, with one pack not operating, the other
pack automatically switches to “high air flow” in order to maintain the necessary
ventilation rate. This automatic switching is inhibited when the airplane is on the
ground, or inflight with the flaps extended, to insure adequate engine power for
single engine operation. Automatic switching to “high air flow” occurs if both
engine bleed air switches are OFF and the APU bleed air switch is ON, regardless
of flap position, air/ground status or number of packs operating.
With the air conditioning pack switch in HIGH, the pack provides “high air flow”.
Additionally, an “APU high air flow” rate is available when the airplane is on the
ground, the APU bleed air switch is ON and either or both pack switches are
positioned to HIGH. This mode is designed to provide the maximum airflow when
the APU is the only source of bleed air.
