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APU
Description
- Sundstrand APS 2300.
- Single stage compressor impeller.
- Two stage axial turbine.
- The gearbox assembly reduces engine speed to drive the 40kVA oil cooled AC generator and the oil pump assembly.
- Uses FADEC. The FADEC also supplies information to the CMC.
Limitations
| Parameter | Min | Max | ||
| Start: | ||||
| Temperature | -54°C | ISA + 35°C | ||
| Altitude | - | 30,000' | ||
| Operation: | ||||
| Temperature | -62°C | ISA + 35°C | ||
| Altitude: | ||||
| Electrical Gen | - | 33,000' | ||
| Bleed | - | 15,000' | ||
| To Assist Engine Start | - | 21,000' | ||
| Rotor Speed | - | 108% | ||
| EGT (1)(2): | ||||
| Start | - | 1032°C | ||
| Continuous | - | 717°C | ||
(1) In flight, there is no automatic shutdown if EGT exceeds the limits.
(2) APU EGT amber indication begins at 667°C. There is no time limitiation for operating the APU in the amber range between 667°C and the continuous limit of 717°C.
APU Start First and Second Cycles ..... 60 sec ON, 60 sec OFF
Third Cycle ..... 60 sec ON, 5 min OFF
Starting
- May be started up to and including 30,000'.
- Started using BATT 2, or a DC GPU.
Start sequence
| APU master switch ON | Powers APU FADEC, opens APU fuel shutoff valve |
| APU master switch START | FADEC energises start controller |
| 7% | FADEC commands fuel module to open and energise the exciter |
| 50% | Ignition exciter and starter deenergised |
| 95% + 3s | Electrical and pneumatic power available |
Operation
- Limited to 33,000'.
- AC power can be supplied up to and including 33,000'.
- Bleed air is provided for engine starting up to 21,000', and for the AMS up to 15,000'.
- Operates at a constant speed.
Shutdown sequence
| APU master switch OFF | Pneumatics removed, APU GEN off-line if it is not the only power source, otherwise remains on-line for whole shutdown |
| 2 minutes* | Fuel module closes, APU off |
| 2.5 minutes | FADEC power removed |
* Some modded APUs have a 1 minute shutdown period.
Automatic shutdown
| Condition | Ground | Flight |
| APU overspeed |  | |
| APU underspeed | | |
| APU fire | |  |
| EGT overtemperature | | |
| High oil temperature | | |
| Low oil pressure | | |
| FADEC critical fault | | |
| Sensor fail | | |
EICAS messages
APU FAIL - for automatic shutdown
APU FAULT - if a major fault is active