When dealing with the engines or APU, you have fire loops to detect fires and fault detection systems to keep them honest. You have two fire bottles for the engines, one of those also covers the APU. Inside the airplane the trash receptacles have fire bottles and the cabin has a set of fire extinguishers. With the rest of the airplane, bleed air looks for things hotter than 250°F and electrical sensors look for things hotter than 150°F. What follows is a list of the systems and another list of various things that can go wrong.
Everything here is from the references shown below, with a few comments in an alternate color.
G450 ECS Synoptic, from Eddie's aircraft.
The procedure is fine until step 1, then it goes all wrong. Remember the prime directive when it comes to abnormal procedures in any GV series airplane: CAS, synoptics, QRH — in that order.
Call for the checklist and while the other pilot is looking for it, you can have all this done. Why the rush? In the best case scenario, a blown duct, having all that hot air back there can make things very bad, very quickly. In the worst case scenario, a fire, you are going to need to get the airplane on the ground very quickly. Do do this while the other pilot gets the checklist out:
AFT EQUIPMENT HOT
Figure: Aft equipment overheat sensors, from Illustrated Parts Catalog, §26-14-00, figure 5.
[G450 MM, §26-14, ¶3.A] The aft equipment switches are installed in the tail compartment at FS 660, near the bleed air ducting. The switches close at 250°F ±5°F. After cooling, the switches will open at 235°F ±5°F. When any of the switches close, the circuit is completed to MAUs No. 1 and No. 2. The MAUs will then generate the Aft Equipment Hot (red) message for display on the CAS. The switches are powered with 28 Vdc from the left essential dc bus through the WARN LTS PWR #2 circuit breaker.
The 250°F switches are located fairly high and forward in the aft equipment bay. The tail compartment access door spans from FS 728 to 770, so those switches (at FS 660) are forward of that. The ambient temperature of the aft equipment during flight is said to be around 70°F, just residual heat from the engine bleed air ducts. If you have a AFT EQUIPMENT HOT indication, you either have a leaking bleed air duct, a fire, or a bad sensor indication.
[G450 Quick Reference Handbook, page MA-3] Aft equipment hot: Aft equipment area temperature above 250°F. Possibility exists that high pressure duct has blown or that fire is in progress.
[G450 Aircraft Operating Manual, §2A-36-20, ¶2.A.]
It should normally be pretty cold back there while in flight. The Aft Equipment Hot CAS message comes on at 250°F so if the message is real, you probably have a blown high pressure duct or there may be a fire. In the case of a blown duct, you need to take the pressure away. In the case of a fire, you need to land immediately.
[G450 Airplane Flight Manual, §04-20-30]
Note: High Turbine Gas Temperature (TGT) or Fuel Flow (FF) indications, low Engine Pressure Ratio (EPR) indication, or an abnormally low BLEED AIR indication may aid in identifying the engine affected with the Aft Equipment Hot message.
CAUTION: ENGINE COWL ANTI-ICE IS NOT AVAILABLE WITH THE ON SIDE ENGINE BLEED AIR SWITCH SELECTED OFF. DEPART ICING CONDITIONS AND AVOID FOR THE REMAINDER OF THE FLIGHT.
This isn't always the case, later G450s have removed the check valve that prevents bleed air coming from outside the engine to reach the cowl anti-ice. This isn't documented (yet).
For more about this, see: G450 Cowl Anti-Ice System.
Do you want to subject the airplane to this stress if there is an unknown problem with a hot bleed air duct back there? The cabin leak rate is said to the around 1,000 feet per minute so you should have at least 4 minutes to get down to a suitable altitude. If you are at 45,000 feet, an emergency descent is probably in order. If you are at 15,000 feet? No so much.
NOTE: This will result in loss of cabin pressurization. Cabin altitude will climb at the cabin leak rate.
The location of the thermal switches make the most probable culprits seemingly obvious:
The switches are triggered at 250°F so a quick look at the synoptic can help you find the problem. The wing anti-ice ducts come right off the bleed air duct set reliably to 400°F or 500°F. A bleed air leak should reduce the temperature of the air actually getting to the wing. I took the photo of the synoptic above on properly operating system. The temperature of the wings is taken at Gap Band #2, about a third the distance outbaord on the wing. If the wing anti-ice controller is unable to get that wing to its 130°F target, a leak on that side could be the issue.
What about the ECS? The trim air valves do have access to that same hot bleed air and should not be discounted as the source of the bleed air leak.
Aft Floor Hot, L-C-R
The temperature under the floor near the ECS ducts/valves and wing anti-ice system ducts/valves has exceeded 250°F. There are three areas: Left, Center, and Right.
[G450 AMM, § 26-14-00 ¶3.A.] The left aft floor switches are installed below the cabin floor on the left side at FS 572, FS 580 and FS 596, near the hot air ducting. The center aft floor switches are installed below the cabin floorat FS 556 and FS 572, near the trim air valves. The right aft floor switches are installed below the cabin floor at FS 540, FS 572 and FS 592, near the hot air ducting.
[G450 AFM, § 4-20-50]
If the Aft Floor Hot, L-R message is displayed, complete Steps 1 through 9. If the Aft Floor Hot, C message is displayed, proceed to Step 10.
Figure: Overheat detection system diagram, from G450 Aircraft Operating Manual, §2A-26-00, figure 6.
These overheat switches are typically set at 150°F. Gulfstream is starting to purge the books of these numbers but it still exists for EER Hot and PDB Overheat. Why do I harp on this? Because 150°F isn't that much.
Dropping the cabin temperature could help a lot. Increasing the cabin altitude to 7,900' is a great idea but don't go any higher. (The CABIN PRESS LOW message is usually set a 8,000' and exceeding it could cause an automatic Emergency Descent.
BAGGAGE EER HOT
PDB OVERHEAT, L-R
Figure: Equipment overheat switch, from G450 Maintenance Manual, §26-14-01, figure 405.
[G450 Maintenance Manual, §26-14-00, ¶3.A.]
The electronic equipment racks are normally cooled with conditioned air and dedicated fans, they shouldn't be too much hotter than the cabin temperature. Increasing the flow of cool air by lowering cabin temperature and increasing air flow and the prescribed solutions. Even if it does cure your overheat, you still need to consider the cause of the overheat. You might have more problems ahead of you.
[G450 Airplane Flight Manual, §3-20-20]
NOTE: For Baggage EER Hot message, inspect compartment loading to ensure that airflow to the electronic equipment is not blocked by luggage or other items.
Raising cabin altitude increases airflow through the TROV
Descending to 33,000 feet or below causes the EER fans to shift to high speed, thereby increasing cooling airflow.
This also kicks the fans cooling the TRU's into low speed mode. If the issue is high draw from a component, you might consider closely monitoring TRU loads to anticipate a TRU overheat.
CAUTION: DO NOT RESET ANY POPPED CIRCUIT BREAKERS.
The good news is Gulfstream put everything in one checklist (EC-8) that leads you to the three other checklists needed as the situation dictates. The bad news is that if you have to read each checklist you might be too late. Statistics show that if you don't put a cabin fire out in eight minutes or less you probably won't and if you don't land the airplane in fifteen minutes or less, you probably won't.
See G450 Cabin Fire.
You might have fire, smoke and fumes; you might also have one of the following CAS messages:
Aft Baggage Flame
Aft Baggage Smoke
Aft Lavatory Flame
Aft Lavatory Smoke
Forward Lavatory Flame
Forward Lavatory Smoke
[G450 QRH, pg. EC-8]
WARNING: DO NOT DELAY DESCENT OR DIVERSION TO FIND THE SMOKE SOURCE. REGARDLESS OF WHETHER A FIRE HAS BEEN EXTINGUISHED OR SMOKE HAS CLEARED, CONSIDERATION SHOULD BE GIVEN TO LANDING THE AIRPLANE WITHOUT DELAY.
WARNING: CONSIDER ALL SMOKE AND/OR FUMES TO BE TOXIC.
WARNING: EXERCISE EXTREME CAUTION WHEN USING OXYGEN NEAR OPEN FLAME.
NOTE: Visually confirm that an oxygen mask has deployed for each passenger. Advise passengers to DON oxygen masks.
If level flight is not critical:
Use of autopilot and autothrottles is recommended. Set altitude preselector to desired safe altitude.
NOTE: See Emergency Descent Procedure, page EH-3. Proceed to the appropriate section to complete checklist:
The QRH makes it clear you need to be thinking and acting in two parallel, simultaneous directions: fight the fire and get the airplane on the ground.
The engine pylon has air circulating from the leading to the trailing edge. The only source of hot air would occur if you had a bleed air leak in the precooler on the lines leading to and from the precooler. This air is under pressure and is very hot. If you have a valid pylon hot message, you need to get rid of the bleed air. If you can't, you are better off shutting the engine down.
[G450 Airplane Flight Manual, §4-20-20]
Figure: Equipment cooling fans, from G450 Aircraft Operating Manual, §2A-21-00, figure 5.
A Forward Floor or TRU Hot message usually portends future electrical problems that might be fixable by non-electrical means. It doesn't take much to cause a TRU Hot message — 150°F — dropping the cabin temperature could help a lot. Increasing the cabin altitude to 7,900' is a great idea but don't go any higher. (The CABIN PRESSURE LOW message is usually set at 8,000' cabin altitude and exceeding it could cause an automatic Emergency Descent.)
Another thing you can do is to climb above 36,000' if you are below it. That will kick the PSU fans to high speed mode.
What else can you do? You know the normal load on your TRU's rarely tops 33% and if you see one that is well above that there are two possibilities. Something on that bus has a high draw or the TRU itself is going bad. If dropping a fuel pump doesn't help, try pulling the circuit breaker for the TRU, you know the load will automatically go to the AUX TRU so what have you got to lose?
You may see some degradation of the TRU's performance on the DC Synoptic, or it may have dropped off line. Of course you should also get a CAS message:
AUX TRU HOT
ESSENTIAL TRU HOT
MAIN TRU HOT
Forward Floor Area Hot
You may have been sent here via the:
35K Altitude Trip Fail
[G450 Airplane Flight Manual, page 03-123] Aux TRU Hot — AUX TRU temperature exceeds maximum allowable temperature.
[G450 Airplane Flight Manual, page 03-131] Essential TRU Hot — Indicated Essential TRU temperature exceeds maximum allowable temperature.
[G450 Airplane Flight Manual, page 03-140] Main TRU Hot — Indicated TRU temperature exceeds maximum allowable temperature.
[G450 Airplane Flight Manual, page 03-134] Forward Floor Area Hot — Forward underfloor area temperature exceeds maximum allowable temperature.
[G450 Airplane Flight Manual, §03-20-10] Cooling air is drawn from the Left and Right Electronic Equipment Rack (LEER) and (REER), aided by the exhaust of the Passenger Service Unit (PSU) fan and routed beneath the forward floor area primarily to cool the five Transformer-Rectifier Units (TRUs): Auxiliary (AUX), Left Essential (L ESS), Right Essential (R ESS), Left Main (L MN) and Right Main (R MN). The amber Forward Floor Area Hot message is displayed on the Crew Advisory System (CAS) when the temperature under the forward cabin floor between the EERs exceeds 150°F. It is likely that an overheat underneath the forward floor area is associated with an overheating Transformer/Rectifier Unit (TRU) and will be accompanied by one of the TRU Hot CAS messages.
The TRU's are located under the forward floor, just inboard of the main entrance door. Any of these messages means one or more of the TRUs may be overheating. The trip point of these switches are not very high, only 150°F. Getting cool, conditioned air over the TRUs may solve what ails you.
[G450 Airplane Flight Manual, page 03-148] 35K Altitude Trip Fail — Relay fails to enable 35,000 feet switchover. EER cooling fans stay in high speed mode while PSU fan stays in low speed mode.
[G450 Maintenance Manual, §21-25-00, ¶3.]
[G450 Maintenance Manual, §21-25-00, ¶4.]
The LEER and REER fans need to be in high speed mode at low altitude while the PSU fans need the higher speed at high altitudes. If either of these fans fail to go into high speed when called for, you might next see a TRU overheat.
[G450 Airplane Flight Manual, § 03-20-10]
Raising cabin altitude increases airflow through the TROV.
What is excessive? We usually see our TRU's in the high twenties, sometimes low thirties. I've never seen a G450 TRU above 38%.
CAUTION: ENSURE THE CROSSFLOW VALVE IS OPEN BEFORE TURNING OFF BOTH BOOST PUMPS ON ONE SIDE TO PROVIDE A SOURCE OF PRESSURIZED FUEL TO THE ENGINE.
You should not set the cabin pressure above 8,000 feet since that will trip the CABIN PRESSURE LOW warning and could cause an automatic emergency descent.
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream G450 Aircraft Operating Manual (Historical), Revision 24, September 18, 2009.
Gulfstream G450 Airplane Flight Manual, Revision 36, December 5, 2013
Gulfstream G450 Illustrated Parts Catalog, Revision 17, October 31, 2012
Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013
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