APU Start Checklist
James Albright (a former G450 driver)
Updated: 2016-07-01
The APU Start Checklist is straight forward, though there are a few checks to be accomplished along the way. Once the APU is providing AC electrical power, the entire airplane will be powered and many of the required checks become possible.
Before you start this jet engine, it might be helpful to consider the APU starter places a tremendous electrical load on your batteries. Unlike the other aircraft in the GV series, the battery switching is quite clever for the G450 APU. The starter load is normally taken by the left battery but the right battery powers the ECU.
There was a 2016 Gulfstream Journal report of a crew that dispatched with an inoperative left battery charger as permitted by the MEL. The APU started okay and they flew to their destination. For the next start the APU never made it past 12% and shut itself down. Incredibly, Gulfstream Technical Ops could only advise them to get an air cart and arranged for the Field and Support Team (FAST) to bring a new charger. The FAST team replaced the charger, charged the battery, and they were good to go. What else could they have done? Unlike the GV and G550, in the G450 they could have simply turned the left battery switch off to start the APU using the right battery. Gulfstream says they will add this to the AFM, AOM, QRH, MEL, and MOPP. A little systems knowledge would have saved the day.
Everything here is from the references shown below, with a few comments in an alternate color.
AFM Procedure
[G450 Aircraft Flight Manual, §2-02-10]
Emergency Power . . . ON
The emergency batteries are now powering the aircraft. Check for the following: pilot's audio control panel, pilot's clock, MCDU #1 shows standby engine instruments, MCDU #3 shows radios, SFD, EBDI, landing gear indicators, and the copilot's clock:
2. Left / Right Batteries . . . ON
Note: Wait until the POWER UP TEST IN PROGRESS is no longer displayed on the Display Controllers before proceeding.
The "ON" capsules will illuminate if there is no other power source for the DC ESS, which should be the case at this point.
3. Batteries Volts . . . Check (22V DC MIN)
Note: If the left battery is below 22V and the right battery is at or above 22V, the left battery must be deselected to utilize the right battery for APU start.
For APU starts following prolonged cold soaks if external AC power is available:
4. External AC . . . ON
CAUTION: PRIOR TO APU START ALLOW BATTERIES TO FULLY CHARGE WITH EXTERNAL AC CONNECTED.
5. DU 1 . . . NORM
[Gulfstream G450 Aircraft Operating Manual, §07-01-20 5.C.(6)] Cockpit systems power up should be delayed until cockpit, cabin, and Electronic Equipment Rack (EER) temperatures have reached approximately +65°F (+18°C). These systems include Display Units (DUs) and Inertial Reference Systems (IRSs). Extreme cold-soaking can cause spurious failure messages and indications on the Crew Advisory System (CAS) until core temperature of control units have reached normal operating temperatures.
If the temperature is less than 65°F, leave the DUs off, conduct the fire test, start the APU, use the bleed air to heat the cockpit, and activate cockpit electrical systems once the temperature is above 65°F.
Scan the list of CAS messages and get to know what you are looking for in general. We get a stack of red and amber followed by one blue. There have been times we saw more ambers which pushed the blue off the list. The aircraft powered up okay but the avionics didn't work correctly and we had to "reboot." We could have done the reboot earlier knowing to check this list first.
6. APU Fire Test . . . PEFORM
Depressing the APU Fire Test switch should cause a three-chime aural warning tone, both Master Warning glare shield switches to illuminate, an exterior fire bell in the nose wheel to sound (ground only), the FIRE light on the APU control panel, a red APU Fire and an amber Fire Detector Fail CAS message annunciation. If the DUs are not powered because of cold temperatures, the requirement to view the CAS messages is understood to be "not possible," though nothing really says this.
7. Fire Bottle Discharge, L-R CAS Message . . . VERIFY NOT DISPLAYED
If the DUs are not powered because of cold temperature and the fire bottle does discharge, the Fire Bottle Discharge message will remain once the DU is powered.
You really need to read through the list of amber CAS messages to check for this item. If you had a thermal discharge of the bottle prior to the test, it will not be flashing.
8. Essential AC-Bus Fail CAS Message . . . VERIFY NOT DISPLAYED
Why are you doing this? You are checking the REAC relay to the AC ESS bus that can only be checked when both AC main buses are unpowered. This check cannot be made if using external AC power since those buses will be powered and can be waived until the next APU test without external AC power.
If the DUs are not powered because of cold temperature, the check can still be made by ensuring the Cabin Pressure Controller panel does not indicate "FAIL," which would happen if the E-Inverter was unable to provide power to the pressurization system because the REAC relay was frozen in position.
You really need to read through the list of amber CAS messages to check for this item. If the REAC relay had failed, it would have been failed prior to the test and would not be flashing at this point.
9. DU 1 . . . OFF
10. MFD Display Switching . . . PILOT / COPILOT = NORM
11. APU AIR . . . OFF
The APU air load control valve is inhibited OFF until 90 seconds after the APU reaches 95% so leaving this switch ON doesn't impact the start.
12. NAV Light . . . ON
13. L MAIN Boost Pump . . . ON
Technique: leave the pump off until after the Ready Light is illuminated the second time, to save battery wear.
14. APU Master Switch . . . ON
The READY light will come on momentarily and then go out as the APU ECU performs a Built-In Test, opens the fuel shutoff valve, and opens the APU inlet door (65° if the engines are not operating, 27° if they are). This should take about 30 seconds.
15. APU READY Light . . . ILLUMINATED
16. APU START . . . PRESS (MOMENTARILY)
Hold the Start Switch for at least a few seconds, the ECU has been known to become confused if the switch is immediately released.
At 5% the fuel control shutoff valve opens and the igniters are energized.
At 7% the READY light extinguishes.
At 50% the ECU disengages the starter and the START switch extinguishes.
At 95% ignition is deactivated.
Four seconds after 95% the APU generator is available and will come on line if the APU Generator switch is in the ON position and the engine generators are off line.
Ninety seconds after 100%, bleed air is available and will be provided if the APU bleed switch is IN. Much of the AOM says 95% but these are starting to change to the more accepted 100%
WHEN APU REACHES OPERATING SPEED (100% RPM):
17. APU GEN . . . ON
NOTE: If the APU GEN switch is already in the ON position when the APU start sequence is initiated, the APU generator will automatically power the bus four (4) seconds after the APU achieves 95% RPM.
This is the normal state for the system, with the APU GEN switch in the ON position.
18. EMERGENCY POWER . . . ARM
WHEN APU IS STABILIZED AT 100% RPM FOR NINETY (90) SECONDS:
19. APU AIR . . . ON
NOTE: The APU air load control valve is inhibited OFF until the APU is stabilized for ninety (90) seconds.
NOTE: When operating in high ambient temperatures (greater than +35°C / 95°F), reduce cabin temperature by selecting full cold in manual mode. Utilize both air conditioning packs, close the main and the external baggage doors, and lower window shades to expedite cooling. Minimize electrical loads until the airplane has cooled down by selecting items such as Display Units, Boost Pumps, and Galley Equipment OFF.
20. L and R Total Air Temperature (TAT) Probes Airflow . . . CHECK
NOTE: Check for proper aspirated airflow at the aft end of the probe. Steady airflow should be present with the APU Air ON. If the airflow is not steady or there is some doubt, maintenance action is recommended prior to flight.
21. External AC (if used for start) . . . OFF
References:
Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013
Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013
Gulfstream G450 Operating Manual Supplement, G-450-OMS-02, Extended Operations (ETOPS) Guide, Revision 2, April 2, 2009
Gulfstream G450 Performance Handbook, GAC-AC-G450-OPS-0003, Revision 20, November 30, 2011
Gulfstream G450 Quick Reference Handbook, GAC-AC-G450-OPS-0003, Revision 34, 18 April 2013
Gulfstream G450 Weight and Balance Manual, Revision 3, March 2008