Large Vacancy Bid Opened - 60 WB CA Slots
10-13-2024 | 01:51 AM
#71
Gets Weekends Off
Joined: Nov 2009
Posts: 5,510
Likes: 110
If you watch the video from a couple of weeks ago where B. Mack goes over all the revisions in the latest FM for the 737 fleet, he explains why we don't run packs and PCA concurrently and according to him it comes directly from Boeing. I don't believe it is going away anytime soon after hearing his explanation, but that is just my opinion.
No.
10-13-2024 | 09:49 AM
#72
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Joined: Apr 2013
Posts: 742
Likes: 41
10-14-2024 | 12:10 AM
#73
On Reserve
Joined: Oct 2021
Posts: 27
Likes: 5
Conditioned air coming out of the air-conditioning ducts can come from 2 sources.
1- Air conditioning packs- The Air Cycle Machine and the various associated components collectively and originally called a package, or pack. Each pack intakes pressurized pnuematic air bled from the compressor section of a turbine engine on the aircraft (Propulsion engines, or from the APU and in case of 787 electirically) called bleed air, flowing into the pnematic system ducts at high pressure and temperature. This air, after being processed into conditioned air, it flows into the cabin.
2- Pre-conditioned air- An external airconditioning system is used to produce conditioned air (cold, hot) to go directly into the airconditioning ducts flowing into the cabin, bypassing the path bleed air takes starting from a turbine compressor, since it's already conditioned.
The packs don't know the difference between the external pneumatic air or pnumatic air from the APU or Engines. The reason behind the restriction at some airlines allowing external pnematic air to run the packs and some not, is the contamination issue. Oil and water mainly. If the ground equipment (external pneumatic air compressor) is maintained up to a certain standard, there's no issue allowing it's compressed air to enter the packs and then the airconditioning ducts and into the cabin beacause its clean. But this requires a proper ground equipment maintenance program, and as always anything proper costs more money. So some airlines don't want to do this and just prohibit it's use. That's all. A pre-conditioned air cart (PCA) will contaminate it's own pack system, not the aircraft's. Much cheaper to fix. Not that PCA's minus the very rare occasions can actually adequately cool an aircraft anyway, but that's another discussion. Also, It seems to be an impossible task to get people to attach the duct without a constriction twist so air can actually get thru. It's hard.
You can have both external pre-conditioned air attached and running, and have the packs running. Both pressurize the same airconditioning ducts flowing into the cabin. There is a check valve which prevents these 2 sources from backflowing each other. BUT, The check valve doesn't do a good enough job of preventing over-pressure occuring in the airconditioning ducts. The 2 sources put out roughly the same pressure air so it can float the check valve leaving it partially open. It still prevents backflow but allowing pressure to rise at the same time. When these ducts are over-pressurized, ruptures happen at the seams where different sections are assembled to make up the duct. Then some air continously escapes from these ruptures and we have an airplane that has trouble cooling even with both packs runnning and all doors closed, sometimes even inflight. This is a hard troubleshoot find and fix for mx, therefore it typically doesn't get fixed until the next heavy mx check. These ducts are not easy to access to see where it needs repairing. Significant dissassembly is required. I've done this job on the line a couple of times, it takes a few shifts. Not enough time on an overnight. Hence prohibition by airlines to not do this double sourcing into the ducts. But if you have one of these airplanes that don't seem to get much air coming out of the vents, the damage is already done, you can't overpressurize the ducts anymore because they have ruptures already. You won't be able to cause anymore damage.
I mentioned over-pressure vs back-flow in air-condition ducts. In comparison on 737 pnuematics, and the prohibition on dual-bleed, there's also a check valve in this sytem to prevent the APU and Engine bleed to backflow each other. This check valve does is able to do much better since there's a significant differemce between APU bleed and Engine bleed on the ground (APU runs at 100% all the time and puts out much higher bleed pressure than engines at or close to idle). Therefore this check valve is firmly closed on the engine bleed side since the APU bleed air pressure is firmly pushing it shut. Nothing happens if you have both APU bleed AND engine bleeds ON at the same time with the eingines and the APU running, and engines at or close to idle. No back-flow, no over-pressure. BUT, if you have only one engine running on 737 which is an underpowered airplane, the running engine WILL need significant thrust to move the airplane which results in much higher bleed pressure from the engine. So airlines that do a lot of single engine taxi like United, don't tell you that it's ok to have dual bleed IF at idle like boeing says, they just say dual bleed no no. They expect your're doing single engine taxi requiring high thrust which results in enging bleed air pressure to rise significantly and getting close to or more than the APU bleed pressure, floating the check valve, which then can allow overpressure of the pneumatic ducts, which will rupture seals, causing pnemantic leaks, most likey resulting in fire warnings from the hot air leaking out of the ducts at some point in the near future. Of course there's the option of a supplementary procedure for hot cabin air to close the engine bleed valves allowing the APU to supply the packs for more effective cooling on the ground, requiring to reset the system to normal config. before a normal engine bleed on takeoff.
Don't overthink it. You have not been given enough informaion to know enough for that. Some have made this comically obvious here with their comments showcasing utter lack of knowlege how the Puematic & Airconditioning systems work on the airplanes they supposedly fly.
Individuals are not to be blamed for not knowing. It's the organization which is at fault. Each person is a product of the organization's training system afterall.
This totally doesn't belong in this thread. But I was so bored...
1- Air conditioning packs- The Air Cycle Machine and the various associated components collectively and originally called a package, or pack. Each pack intakes pressurized pnuematic air bled from the compressor section of a turbine engine on the aircraft (Propulsion engines, or from the APU and in case of 787 electirically) called bleed air, flowing into the pnematic system ducts at high pressure and temperature. This air, after being processed into conditioned air, it flows into the cabin.
2- Pre-conditioned air- An external airconditioning system is used to produce conditioned air (cold, hot) to go directly into the airconditioning ducts flowing into the cabin, bypassing the path bleed air takes starting from a turbine compressor, since it's already conditioned.
The packs don't know the difference between the external pneumatic air or pnumatic air from the APU or Engines. The reason behind the restriction at some airlines allowing external pnematic air to run the packs and some not, is the contamination issue. Oil and water mainly. If the ground equipment (external pneumatic air compressor) is maintained up to a certain standard, there's no issue allowing it's compressed air to enter the packs and then the airconditioning ducts and into the cabin beacause its clean. But this requires a proper ground equipment maintenance program, and as always anything proper costs more money. So some airlines don't want to do this and just prohibit it's use. That's all. A pre-conditioned air cart (PCA) will contaminate it's own pack system, not the aircraft's. Much cheaper to fix. Not that PCA's minus the very rare occasions can actually adequately cool an aircraft anyway, but that's another discussion. Also, It seems to be an impossible task to get people to attach the duct without a constriction twist so air can actually get thru. It's hard.
You can have both external pre-conditioned air attached and running, and have the packs running. Both pressurize the same airconditioning ducts flowing into the cabin. There is a check valve which prevents these 2 sources from backflowing each other. BUT, The check valve doesn't do a good enough job of preventing over-pressure occuring in the airconditioning ducts. The 2 sources put out roughly the same pressure air so it can float the check valve leaving it partially open. It still prevents backflow but allowing pressure to rise at the same time. When these ducts are over-pressurized, ruptures happen at the seams where different sections are assembled to make up the duct. Then some air continously escapes from these ruptures and we have an airplane that has trouble cooling even with both packs runnning and all doors closed, sometimes even inflight. This is a hard troubleshoot find and fix for mx, therefore it typically doesn't get fixed until the next heavy mx check. These ducts are not easy to access to see where it needs repairing. Significant dissassembly is required. I've done this job on the line a couple of times, it takes a few shifts. Not enough time on an overnight. Hence prohibition by airlines to not do this double sourcing into the ducts. But if you have one of these airplanes that don't seem to get much air coming out of the vents, the damage is already done, you can't overpressurize the ducts anymore because they have ruptures already. You won't be able to cause anymore damage.
I mentioned over-pressure vs back-flow in air-condition ducts. In comparison on 737 pnuematics, and the prohibition on dual-bleed, there's also a check valve in this sytem to prevent the APU and Engine bleed to backflow each other. This check valve does is able to do much better since there's a significant differemce between APU bleed and Engine bleed on the ground (APU runs at 100% all the time and puts out much higher bleed pressure than engines at or close to idle). Therefore this check valve is firmly closed on the engine bleed side since the APU bleed air pressure is firmly pushing it shut. Nothing happens if you have both APU bleed AND engine bleeds ON at the same time with the eingines and the APU running, and engines at or close to idle. No back-flow, no over-pressure. BUT, if you have only one engine running on 737 which is an underpowered airplane, the running engine WILL need significant thrust to move the airplane which results in much higher bleed pressure from the engine. So airlines that do a lot of single engine taxi like United, don't tell you that it's ok to have dual bleed IF at idle like boeing says, they just say dual bleed no no. They expect your're doing single engine taxi requiring high thrust which results in enging bleed air pressure to rise significantly and getting close to or more than the APU bleed pressure, floating the check valve, which then can allow overpressure of the pneumatic ducts, which will rupture seals, causing pnemantic leaks, most likey resulting in fire warnings from the hot air leaking out of the ducts at some point in the near future. Of course there's the option of a supplementary procedure for hot cabin air to close the engine bleed valves allowing the APU to supply the packs for more effective cooling on the ground, requiring to reset the system to normal config. before a normal engine bleed on takeoff.
Don't overthink it. You have not been given enough informaion to know enough for that. Some have made this comically obvious here with their comments showcasing utter lack of knowlege how the Puematic & Airconditioning systems work on the airplanes they supposedly fly.
Individuals are not to be blamed for not knowing. It's the organization which is at fault. Each person is a product of the organization's training system afterall.
This totally doesn't belong in this thread. But I was so bored...
10-14-2024 | 03:37 PM
#76
Line Holder
Joined: Apr 2013
Posts: 742
Likes: 41
Conditioned air coming out of the air-conditioning ducts can come from 2 sources.
1- Air conditioning packs- The Air Cycle Machine and the various associated components collectively and originally called a package, or pack. Each pack intakes pressurized pnuematic air bled from the compressor section of a turbine engine on the aircraft (Propulsion engines, or from the APU and in case of 787 electirically) called bleed air, flowing into the pnematic system ducts at high pressure and temperature. This air, after being processed into conditioned air, it flows into the cabin.
2- Pre-conditioned air- An external airconditioning system is used to produce conditioned air (cold, hot) to go directly into the airconditioning ducts flowing into the cabin, bypassing the path bleed air takes starting from a turbine compressor, since it's already conditioned.
The packs don't know the difference between the external pneumatic air or pnumatic air from the APU or Engines. The reason behind the restriction at some airlines allowing external pnematic air to run the packs and some not, is the contamination issue. Oil and water mainly. If the ground equipment (external pneumatic air compressor) is maintained up to a certain standard, there's no issue allowing it's compressed air to enter the packs and then the airconditioning ducts and into the cabin beacause its clean. But this requires a proper ground equipment maintenance program, and as always anything proper costs more money. So some airlines don't want to do this and just prohibit it's use. That's all. A pre-conditioned air cart (PCA) will contaminate it's own pack system, not the aircraft's. Much cheaper to fix. Not that PCA's minus the very rare occasions can actually adequately cool an aircraft anyway, but that's another discussion. Also, It seems to be an impossible task to get people to attach the duct without a constriction twist so air can actually get thru. It's hard.
You can have both external pre-conditioned air attached and running, and have the packs running. Both pressurize the same airconditioning ducts flowing into the cabin. There is a check valve which prevents these 2 sources from backflowing each other. BUT, The check valve doesn't do a good enough job of preventing over-pressure occuring in the airconditioning ducts. The 2 sources put out roughly the same pressure air so it can float the check valve leaving it partially open. It still prevents backflow but allowing pressure to rise at the same time. When these ducts are over-pressurized, ruptures happen at the seams where different sections are assembled to make up the duct. Then some air continously escapes from these ruptures and we have an airplane that has trouble cooling even with both packs runnning and all doors closed, sometimes even inflight. This is a hard troubleshoot find and fix for mx, therefore it typically doesn't get fixed until the next heavy mx check. These ducts are not easy to access to see where it needs repairing. Significant dissassembly is required. I've done this job on the line a couple of times, it takes a few shifts. Not enough time on an overnight. Hence prohibition by airlines to not do this double sourcing into the ducts. But if you have one of these airplanes that don't seem to get much air coming out of the vents, the damage is already done, you can't overpressurize the ducts anymore because they have ruptures already. You won't be able to cause anymore damage.
I mentioned over-pressure vs back-flow in air-condition ducts. In comparison on 737 pnuematics, and the prohibition on dual-bleed, there's also a check valve in this sytem to prevent the APU and Engine bleed to backflow each other. This check valve does is able to do much better since there's a significant differemce between APU bleed and Engine bleed on the ground (APU runs at 100% all the time and puts out much higher bleed pressure than engines at or close to idle). Therefore this check valve is firmly closed on the engine bleed side since the APU bleed air pressure is firmly pushing it shut. Nothing happens if you have both APU bleed AND engine bleeds ON at the same time with the eingines and the APU running, and engines at or close to idle. No back-flow, no over-pressure. BUT, if you have only one engine running on 737 which is an underpowered airplane, the running engine WILL need significant thrust to move the airplane which results in much higher bleed pressure from the engine. So airlines that do a lot of single engine taxi like United, don't tell you that it's ok to have dual bleed IF at idle like boeing says, they just say dual bleed no no. They expect your're doing single engine taxi requiring high thrust which results in enging bleed air pressure to rise significantly and getting close to or more than the APU bleed pressure, floating the check valve, which then can allow overpressure of the pneumatic ducts, which will rupture seals, causing pnemantic leaks, most likey resulting in fire warnings from the hot air leaking out of the ducts at some point in the near future. Of course there's the option of a supplementary procedure for hot cabin air to close the engine bleed valves allowing the APU to supply the packs for more effective cooling on the ground, requiring to reset the system to normal config. before a normal engine bleed on takeoff.
Don't overthink it. You have not been given enough informaion to know enough for that. Some have made this comically obvious here with their comments showcasing utter lack of knowlege how the Puematic & Airconditioning systems work on the airplanes they supposedly fly.
Individuals are not to be blamed for not knowing. It's the organization which is at fault. Each person is a product of the organization's training system afterall.
This totally doesn't belong in this thread. But I was so bored...
1- Air conditioning packs- The Air Cycle Machine and the various associated components collectively and originally called a package, or pack. Each pack intakes pressurized pnuematic air bled from the compressor section of a turbine engine on the aircraft (Propulsion engines, or from the APU and in case of 787 electirically) called bleed air, flowing into the pnematic system ducts at high pressure and temperature. This air, after being processed into conditioned air, it flows into the cabin.
2- Pre-conditioned air- An external airconditioning system is used to produce conditioned air (cold, hot) to go directly into the airconditioning ducts flowing into the cabin, bypassing the path bleed air takes starting from a turbine compressor, since it's already conditioned.
The packs don't know the difference between the external pneumatic air or pnumatic air from the APU or Engines. The reason behind the restriction at some airlines allowing external pnematic air to run the packs and some not, is the contamination issue. Oil and water mainly. If the ground equipment (external pneumatic air compressor) is maintained up to a certain standard, there's no issue allowing it's compressed air to enter the packs and then the airconditioning ducts and into the cabin beacause its clean. But this requires a proper ground equipment maintenance program, and as always anything proper costs more money. So some airlines don't want to do this and just prohibit it's use. That's all. A pre-conditioned air cart (PCA) will contaminate it's own pack system, not the aircraft's. Much cheaper to fix. Not that PCA's minus the very rare occasions can actually adequately cool an aircraft anyway, but that's another discussion. Also, It seems to be an impossible task to get people to attach the duct without a constriction twist so air can actually get thru. It's hard.
You can have both external pre-conditioned air attached and running, and have the packs running. Both pressurize the same airconditioning ducts flowing into the cabin. There is a check valve which prevents these 2 sources from backflowing each other. BUT, The check valve doesn't do a good enough job of preventing over-pressure occuring in the airconditioning ducts. The 2 sources put out roughly the same pressure air so it can float the check valve leaving it partially open. It still prevents backflow but allowing pressure to rise at the same time. When these ducts are over-pressurized, ruptures happen at the seams where different sections are assembled to make up the duct. Then some air continously escapes from these ruptures and we have an airplane that has trouble cooling even with both packs runnning and all doors closed, sometimes even inflight. This is a hard troubleshoot find and fix for mx, therefore it typically doesn't get fixed until the next heavy mx check. These ducts are not easy to access to see where it needs repairing. Significant dissassembly is required. I've done this job on the line a couple of times, it takes a few shifts. Not enough time on an overnight. Hence prohibition by airlines to not do this double sourcing into the ducts. But if you have one of these airplanes that don't seem to get much air coming out of the vents, the damage is already done, you can't overpressurize the ducts anymore because they have ruptures already. You won't be able to cause anymore damage.
I mentioned over-pressure vs back-flow in air-condition ducts. In comparison on 737 pnuematics, and the prohibition on dual-bleed, there's also a check valve in this sytem to prevent the APU and Engine bleed to backflow each other. This check valve does is able to do much better since there's a significant differemce between APU bleed and Engine bleed on the ground (APU runs at 100% all the time and puts out much higher bleed pressure than engines at or close to idle). Therefore this check valve is firmly closed on the engine bleed side since the APU bleed air pressure is firmly pushing it shut. Nothing happens if you have both APU bleed AND engine bleeds ON at the same time with the eingines and the APU running, and engines at or close to idle. No back-flow, no over-pressure. BUT, if you have only one engine running on 737 which is an underpowered airplane, the running engine WILL need significant thrust to move the airplane which results in much higher bleed pressure from the engine. So airlines that do a lot of single engine taxi like United, don't tell you that it's ok to have dual bleed IF at idle like boeing says, they just say dual bleed no no. They expect your're doing single engine taxi requiring high thrust which results in enging bleed air pressure to rise significantly and getting close to or more than the APU bleed pressure, floating the check valve, which then can allow overpressure of the pneumatic ducts, which will rupture seals, causing pnemantic leaks, most likey resulting in fire warnings from the hot air leaking out of the ducts at some point in the near future. Of course there's the option of a supplementary procedure for hot cabin air to close the engine bleed valves allowing the APU to supply the packs for more effective cooling on the ground, requiring to reset the system to normal config. before a normal engine bleed on takeoff.
Don't overthink it. You have not been given enough informaion to know enough for that. Some have made this comically obvious here with their comments showcasing utter lack of knowlege how the Puematic & Airconditioning systems work on the airplanes they supposedly fly.
Individuals are not to be blamed for not knowing. It's the organization which is at fault. Each person is a product of the organization's training system afterall.
This totally doesn't belong in this thread. But I was so bored...
10-15-2024 | 05:46 AM
#79
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Joined: Jul 2018
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