Loss Of Pressurization At High Altitude
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Loss Of Pressurization At High Altitude
Hi,
I get some questions regarding the loss of pressurization (not sudden decompression) at HIGH ALTITUDE due to all engines flame-out (even the APU will not be able to provide air unless at low altitude):
1-So during depressurization how long the oxygen will be available for the passengers from cruise altitude (modern aircrafts are flying above 40000ft, for certain aircraft like 747 the max certified ceiling is 45100 ft) to a safe altitude? We suppose the aircraft have a normal air leakage rate.
A safe altitude will be 14000 or 10000 ft?
Will the quantity of oxygen be enough for passengers?
2-In such case, I guess the crew will perform emergency descent: how long it take to reach a safe altitude?
Will pilots try to restart engines during the emergency descent?
Can the attempt to restart engines affect the emergengy descent (the rate of descent)?
3-From a safe altitude to the landing, how air is provided to passengers and crew? We suppose engines and APU still off.
4- How air is provided for the flight crew during an unpressurized ferry flight and without oxygen? (engines operating of course).
5-And finally the last question: the aft outflow valve in the 737-NG is thrust recovery??? does it mean that the valve is providing thrust by taking advantage of the difference of air pressure between the pressurized zone in the aircraft and the ambient air??? or it means other thing. By the way this valve is fitted with 2 gates: aft gate and forward gate.
Your feedback will be very appreciated. Thank you in advance.
Best regards.
P.S: I guess the problem will be worst in case of rapid decompression at high altitudes (40000 ft or above) since the oxygen masks (even pilots masks I guess are not pressure feeded O2) are not supplied with "forced" oxygen.
I get some questions regarding the loss of pressurization (not sudden decompression) at HIGH ALTITUDE due to all engines flame-out (even the APU will not be able to provide air unless at low altitude):
1-So during depressurization how long the oxygen will be available for the passengers from cruise altitude (modern aircrafts are flying above 40000ft, for certain aircraft like 747 the max certified ceiling is 45100 ft) to a safe altitude? We suppose the aircraft have a normal air leakage rate.
A safe altitude will be 14000 or 10000 ft?
Will the quantity of oxygen be enough for passengers?
2-In such case, I guess the crew will perform emergency descent: how long it take to reach a safe altitude?
Will pilots try to restart engines during the emergency descent?
Can the attempt to restart engines affect the emergengy descent (the rate of descent)?
3-From a safe altitude to the landing, how air is provided to passengers and crew? We suppose engines and APU still off.
4- How air is provided for the flight crew during an unpressurized ferry flight and without oxygen? (engines operating of course).
5-And finally the last question: the aft outflow valve in the 737-NG is thrust recovery??? does it mean that the valve is providing thrust by taking advantage of the difference of air pressure between the pressurized zone in the aircraft and the ambient air??? or it means other thing. By the way this valve is fitted with 2 gates: aft gate and forward gate.
Your feedback will be very appreciated. Thank you in advance.
Best regards.
P.S: I guess the problem will be worst in case of rapid decompression at high altitudes (40000 ft or above) since the oxygen masks (even pilots masks I guess are not pressure feeded O2) are not supplied with "forced" oxygen.
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Hi,
Thank you Mike for your post.
Old Smokey, I didn't get your answer
I am still waiting 
In addition to the questions regarding the loss of the pressurization (I expected many answers, but I get only one), here are others questions, but please don't disappoint me)
How air is provided for the passengers and flight crew at safe altitude? (how the aircraft get air for the ventilation or from which air inlet ?). An open outflow valve will be an air outlet for the ventilation
How air is provided during an unpressurized ferry flight, without oxygen, and engines operating of course? (this question is not the same context of the subject since engines are operating)
I am asking these 2 last questions, because it seems that Boeing aircrafts are not fitted with a ram air scoop which can provide air for ventilation if the bleed air is not available or 2 packs are not operating (Airbus aircrafts are fitted with these scoops).
In case of cabin smoke, I read somewhere that the sliding windows in the cockpit and the cabin doors can be opened (slightly and aircraft depressurized) to clear smoke in certains Boeing aircrafts (I don't know about Airbus aircrafts), is this true? is this procedure applied for aircraft ventilation?
Any feedback is very appreciated.
Thank you.
Best regards.
Thank you Mike for your post.
Old Smokey, I didn't get your answer
I am still waiting In addition to the questions regarding the loss of the pressurization (I expected many answers, but I get only one
), here are others questions, but please don't disappoint me)How air is provided for the passengers and flight crew at safe altitude? (how the aircraft get air for the ventilation or from which air inlet ?). An open outflow valve will be an air outlet for the ventilation
How air is provided during an unpressurized ferry flight, without oxygen, and engines operating of course? (this question is not the same context of the subject since engines are operating)
I am asking these 2 last questions, because it seems that Boeing aircrafts are not fitted with a ram air scoop which can provide air for ventilation if the bleed air is not available or 2 packs are not operating (Airbus aircrafts are fitted with these scoops).
In case of cabin smoke, I read somewhere that the sliding windows in the cockpit and the cabin doors can be opened (slightly and aircraft depressurized) to clear smoke in certains Boeing aircrafts (I don't know about Airbus aircrafts), is this true? is this procedure applied for aircraft ventilation?
Any feedback is very appreciated.
Thank you.
Best regards.
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Hi,
Mike, thanks for your answer.
Originally posted by Mike
Mike, my question was related to all engines flame-out and APU off due to fuel depletion (I think you forget that). So the engines will not provide bleed air. That's why I was wondering how the aircraft will get air (for the ventilation) for the passengers at safe altitude (10,000 or 14,000 ft) mainly on Boeing aircrafts since they are not fitted with ram air scoop?
-What about Boeing ETOPS aircrafts (let's say 180 or 207 minutes): how the ventilation air will be provided to the all passengers during all this long diversion time ?(Usually chemical generator oxygen systems produce oxygen for 12-15 minutes, may be more few minutes for ETOPS aircrafts). Could the lack of ventilation air affect the health of passengers or provoke suffocation? It will be very helpful if someone can post the checklist of loss of thrust on both engines or loss of pressurization (or other checklist related to the subject mainly in ETOPS aircrafts like 757, 767, 777 that have longer diversion time).
-Consider we have now all engines flame-out at high altitude (BUT not caused by fuel depletion) and the APU is operating:
What you (as pilot) will do first ? (loss of thrust on both engines or loss pf pressurization checklist?)
Feedback very appreciated. Thank you in advance for your help.
Best regards.
Mike, thanks for your answer.
Originally posted by Mike
In simple terms (& depending on aircraft type) air is tapped off from the engines (& cooled as necessary) & enters into the aircraft. The aircraft has a maximum pressure differential permitted between the outside pressure (say at 35,000 ft) & inside (generally kept at about 6000 - 8000 ft for comfort). To prevent too much pressure building up in the aircraft, outflow valves are controlled automatically to keep the required cabin altitude
-What about Boeing ETOPS aircrafts (let's say 180 or 207 minutes): how the ventilation air will be provided to the all passengers during all this long diversion time ?(Usually chemical generator oxygen systems produce oxygen for 12-15 minutes, may be more few minutes for ETOPS aircrafts). Could the lack of ventilation air affect the health of passengers or provoke suffocation? It will be very helpful if someone can post the checklist of loss of thrust on both engines or loss of pressurization (or other checklist related to the subject mainly in ETOPS aircrafts like 757, 767, 777 that have longer diversion time).
-Consider we have now all engines flame-out at high altitude (BUT not caused by fuel depletion) and the APU is operating:
What you (as pilot) will do first ? (loss of thrust on both engines or loss pf pressurization checklist?)
Feedback very appreciated. Thank you in advance for your help.
Best regards.
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AeroTech
The questions you ask? Your questions do not appear aircraft specific which makes it very difficult to answer.....
747 all engines flame out and you are worried about decompression..No 747-400 have APU inflight start so forget that.
Surely the rate of decent depends on the amout of oxygen available. ie Some 747s have extra oxy fitted for crew and pax so when flying over mountainous areas they can remain at altitude longer until a safer altitude becomes available..no cumilous granitous around..
APUs rarely if ever supply bleed air in the air. They provide electrical power
On a unpressurised ferry flight...The airconditioning pac s will still be running just the out flow valves open ...no diff pressure but plenty of flow thru...same as when the aircraft is on the ground..pac s running..
Crew oxy masks not pressure fed? How do you think they get oxy to the mask.
ETOPS DIVERSION. ETOPs is flying on one engine. one engine will provide enough bleed air to keep the aircraft pressurised. No oxygen is required. If you lose an engine and have a decompression. Multiple failures it is a very bad day and if you are on the edge of your ETOPS range you may not make it to your designated diversion airfield.
Why so many questions..What are you learning?
The questions you ask? Your questions do not appear aircraft specific which makes it very difficult to answer.....
747 all engines flame out and you are worried about decompression..No 747-400 have APU inflight start so forget that.
Surely the rate of decent depends on the amout of oxygen available. ie Some 747s have extra oxy fitted for crew and pax so when flying over mountainous areas they can remain at altitude longer until a safer altitude becomes available..no cumilous granitous around..
APUs rarely if ever supply bleed air in the air. They provide electrical power
On a unpressurised ferry flight...The airconditioning pac s will still be running just the out flow valves open ...no diff pressure but plenty of flow thru...same as when the aircraft is on the ground..pac s running..
Crew oxy masks not pressure fed? How do you think they get oxy to the mask.
ETOPS DIVERSION. ETOPs is flying on one engine. one engine will provide enough bleed air to keep the aircraft pressurised. No oxygen is required. If you lose an engine and have a decompression. Multiple failures it is a very bad day and if you are on the edge of your ETOPS range you may not make it to your designated diversion airfield.
Why so many questions..What are you learning?
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Not really Bolty,
ETOP's makes allowance for single engine diversions within its rules, but it is not simply about flying on one engine as you can see from the critical fuel scenarios (item 1) as follows.
ETOPS fuel requirements in additional to the normal fuel requirements require that 3 critical fuel scenarios are taken into account, and that each of these 3 scenarios permit a low level diversion to a suitable diversion airport with the normal holding and approach allowances intact.
The scenarios are :
1) Total pressurisation failure.
Immediate descent and 2 engine cruise to diversion at 10,000ft
2) Engine failure.
Descent to stabilising altitude and single engine cruise to the descent point for landing at the diversion airport.
3) Engine failure and simultaneous pressurisation failure.
Immediate descent to 10,000ft and single engine cruise to the descent point for the diversion airport.
Invariably of course from a fuel critical scenario case 1 is the most critical, and is covered by the normal ETOP's planning rules. However multiple failure case 3 is also covered and would not as you suggest result in not being able to make your diversion airport, unless you had failed to comply with the ETOP's planning rules.
As you say the single engine situation would result in a descent to a stabilising altitude that is mass dependent. Probably somewhere in the low to mid 20's (x 1000 ft). At these altitudes / levels the one engine has much less bleed demand to operate the packs and pressurisation is not normally a problem. I am a bit lost as to Aerotechs point, since if both engines fail ETOP's is a bit of a moot point !
ETOP's makes allowance for single engine diversions within its rules, but it is not simply about flying on one engine as you can see from the critical fuel scenarios (item 1) as follows.
ETOPS fuel requirements in additional to the normal fuel requirements require that 3 critical fuel scenarios are taken into account, and that each of these 3 scenarios permit a low level diversion to a suitable diversion airport with the normal holding and approach allowances intact.
The scenarios are :
1) Total pressurisation failure.
Immediate descent and 2 engine cruise to diversion at 10,000ft
2) Engine failure.
Descent to stabilising altitude and single engine cruise to the descent point for landing at the diversion airport.
3) Engine failure and simultaneous pressurisation failure.
Immediate descent to 10,000ft and single engine cruise to the descent point for the diversion airport.
Invariably of course from a fuel critical scenario case 1 is the most critical, and is covered by the normal ETOP's planning rules. However multiple failure case 3 is also covered and would not as you suggest result in not being able to make your diversion airport, unless you had failed to comply with the ETOP's planning rules.
As you say the single engine situation would result in a descent to a stabilising altitude that is mass dependent. Probably somewhere in the low to mid 20's (x 1000 ft). At these altitudes / levels the one engine has much less bleed demand to operate the packs and pressurisation is not normally a problem. I am a bit lost as to Aerotechs point, since if both engines fail ETOP's is a bit of a moot point !
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You are quite right Bealzebub
I was being vague about ETOPS but it was for errotechs sake.
As his questions about diversion change from engine out to loss of pressurisation. Aircraft also divert due to full toilet tanks but that question hasn't been muddled into this thread yet.
BUT if you have an engine failure on a light twin ,757,767,A330 etc and also a loss of cabin pressure therefore decend to 10k feet to keep pax alive and you are at 179 mins flying from nearest diversion(this 179 minutes is calculated at criusing alt) there is a high possibility that the aircraft will not enough fuel on board to fly this distance.Depends what flight phase you are in when these disasters strike But we are talking about 2 or 3 major failures happing at once...A very bad day at the office.
I have fueled planes ( 767) for non pressurised ferry.
eg Normal fuel for trip with pax cargo around 13,000kgs unpressurised ferry trip no pax no cargo... 20,000kgs of fuel
Hope i appear less vague this time
Bolty
Question for Aerotech.. Are you a big MS Flight Sim fan??
I was being vague about ETOPS but it was for errotechs sake.
As his questions about diversion change from engine out to loss of pressurisation. Aircraft also divert due to full toilet tanks but that question hasn't been muddled into this thread yet.
BUT if you have an engine failure on a light twin ,757,767,A330 etc and also a loss of cabin pressure therefore decend to 10k feet to keep pax alive and you are at 179 mins flying from nearest diversion(this 179 minutes is calculated at criusing alt) there is a high possibility that the aircraft will not enough fuel on board to fly this distance.Depends what flight phase you are in when these disasters strike But we are talking about 2 or 3 major failures happing at once...A very bad day at the office.
I have fueled planes ( 767) for non pressurised ferry.
eg Normal fuel for trip with pax cargo around 13,000kgs unpressurised ferry trip no pax no cargo... 20,000kgs of fuel
Hope i appear less vague this time
Bolty
Question for Aerotech.. Are you a big MS Flight Sim fan??
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"BUT if you have an engine failure on a light twin ,757,767,A330 etc and also a loss of cabin pressure therefore decend to 10k feet to keep pax alive and you are at 179 mins flying from nearest diversion(this 179 minutes is calculated at criusing alt) there is a high possibility that the aircraft will not enough fuel on board to fly this distance.Depends what flight phase you are in when these disasters strike But we are talking about 2 or 3 major failures happing at once...A very bad day at the office."
Yes bolty, but that was my point. The Etops fuel requirements assume that in the worst case scenario you do have a pressurisation failure descend to 10,000ft and divert to your ETOPs alternate at 10,000ft whilst still arriving there with your normal holding reserves intact. Ironicaly perhaps the engine failure and pressurisation case would actually leave you better off since only one engine is using fuel at this altitude. However that notwithstanding and using your 180 minute assumption, you would even in the worst possible scenario still arive at your alternate with 30 minutes holding reserves. If you see what I mean. So it wouldn't be as critical as you suggest. Having said that I don't want to put it to the test, but I am sure you take the point. The fuel is Not calculated at cruising altitude but at 10,000ft. ( see items 1 and 3 )
Yes bolty, but that was my point. The Etops fuel requirements assume that in the worst case scenario you do have a pressurisation failure descend to 10,000ft and divert to your ETOPs alternate at 10,000ft whilst still arriving there with your normal holding reserves intact. Ironicaly perhaps the engine failure and pressurisation case would actually leave you better off since only one engine is using fuel at this altitude. However that notwithstanding and using your 180 minute assumption, you would even in the worst possible scenario still arive at your alternate with 30 minutes holding reserves. If you see what I mean. So it wouldn't be as critical as you suggest. Having said that I don't want to put it to the test, but I am sure you take the point. The fuel is Not calculated at cruising altitude but at 10,000ft. ( see items 1 and 3 )
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Emergency descent and glideslope
A quection related to those: how much energy is wasted by emergency descent to safe altitudes like 10 000 feet?
An airplane famously glided 85 miles horizontally to Azores with no fuel.
Is rapid descent to 10 000 feet or so a good way to stretch out the remaining glideslope, and how long would it take to glide at a maximally stretched-out glideslope from, say 40 000 feet to 25 000 feet?
An airplane famously glided 85 miles horizontally to Azores with no fuel.
Is rapid descent to 10 000 feet or so a good way to stretch out the remaining glideslope, and how long would it take to glide at a maximally stretched-out glideslope from, say 40 000 feet to 25 000 feet?
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Bealzebub
I do indeed take your point and understand it to the fullest. I stand corrected until i read otherwise
I don't fly so my only experience with fuel consumption of an aircraft flying at an unpressurised altitude is the example I gave before..
Bear with me.....
Normal fuel load for the sector with pax and cargo 13,000 kgs
Ferry flight no pax or cargo flying 10,000 feet same sector fuel required was approx 20,000 kgs
I think blind Freddy would draw the same conclusion in that best fuel consumption is very much dependant of the most efficient operating altitude and it would appear 10,000 feet is not the most efficient altitude.
If you have an engine failure on the a "light twin" the operating engine goes to a thrust setting very close to max continuous...burning lots of fuel. You burn more fuel at see level for a given epr than altitude due to fuel metering at a ratio approx 8:1 weight air to fuel( i hope we agree).
E.G. doing a trim run on a 767 for an hour at sea level (part power setting, this is below max continuous) will easily burn 10,000 kgs of fuel in an hour . In 179 minutes you will burn at sea level approx 30,000 ks of fuel. If a 767 fully fuelled to 68,000 kgs and has failures, engine out and pressurisation loss in the later half of the flight.
There may be a problem reaching your diversion point.....
I admit I assumed.
You have wet my appetite. Now I will have to find the absolute answer to this...
Bolty
I do indeed take your point and understand it to the fullest. I stand corrected until i read otherwise
I don't fly so my only experience with fuel consumption of an aircraft flying at an unpressurised altitude is the example I gave before..
Bear with me.....
Normal fuel load for the sector with pax and cargo 13,000 kgs
Ferry flight no pax or cargo flying 10,000 feet same sector fuel required was approx 20,000 kgs
I think blind Freddy would draw the same conclusion in that best fuel consumption is very much dependant of the most efficient operating altitude and it would appear 10,000 feet is not the most efficient altitude.
If you have an engine failure on the a "light twin" the operating engine goes to a thrust setting very close to max continuous...burning lots of fuel. You burn more fuel at see level for a given epr than altitude due to fuel metering at a ratio approx 8:1 weight air to fuel( i hope we agree).
E.G. doing a trim run on a 767 for an hour at sea level (part power setting, this is below max continuous) will easily burn 10,000 kgs of fuel in an hour . In 179 minutes you will burn at sea level approx 30,000 ks of fuel. If a 767 fully fuelled to 68,000 kgs and has failures, engine out and pressurisation loss in the later half of the flight.
There may be a problem reaching your diversion point.....
I admit I assumed.
You have wet my appetite. Now I will have to find the absolute answer to this...
Bolty
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Hi,
Thank you guys for your posts.
I apologize for the confusion. I try to clarify, here is the introduction of the problem (or the scenario):
Boeing (not DC or MD) aircrafts are not fitted with ram air scoop at the opposite of Airbus or McDonnel Douglas aircrafts.
This ram air scoop provides alternate air if there is no engines bleed air or the pack valveS (I mean ALL the flow control valveS) are faulty. I supposed 2 separate scenarios: all engineS flame-out caused by fuel depletion and all engineS flame-out without fuel depletion. All engineS flame-out occured at high altitude (cruise altitude). The all engines flame-out will provoke a gradual loss of pressurization (depending of the air leakage) because there is no engines bleed air. So here, we are not talking about a rapid decompression. The all engines flame-out occured before, either with or without fuel depletion (Gimly glider B767 , Air transat A330, B747 flying through volcanic ash clouds). We suppose that all engines flame-out will occur at cruise altitude in ETOPS aircrafts with 180 or 207 minutes diversion time.
I hope things are clear now and this scenario is plausible. If so, here my questions:
-Consider we have all engines flame-out (caused by fuel depletion) on Boeing ETOPS aircrafts with 180 or 207 minutes and without ram air scoop like B 757, 767, 777): how the ventilation air (without air inlet) will be provided to the all passengers during all this long diversion time at safe altitude (10,000 or 14,000 ft) mainly on Boeing aircrafts since they are not fitted with ram air scoop? (Usually chemical generator oxygen systems produce oxygen for 12-15 minutes during descent, may be more few minutes for ETOPS aircrafts).
-Could the lack of ventilation air affect the health of passengers or provoke suffocation?
It will be very helpful if someone can post the checklist of loss of thrust on both engines or loss of pressurization (or other checklist related to the subject) to figure out how ventilation air is provided mainly in ETOPS aircrafts like 757, 767, 777 that have longer diversion time.
-Consider we have all engines flame-out at cruise altitude ( caused by fuel depletion):
What you (as pilot) will do first ? (loss of thrust on both engines or loss pf pressurization checklist?) Can you please talk about the checklist on the aircraft that you fly or your know (to don't specify the kind aircraft).
-Consider we have now all engines flame-out at cruise altitude (BUT not caused by fuel depletion) and the APU is operating:
What you (as pilot) will do first ? (loss of thrust on both engines or loss pf pressurization checklist?) Can you please talk about the checklist on the aircraft that you fly or your know (to don't specify the kind aircraft).
Feedback very appreciated, thank you in advance for your help and your patience to read this long post.
Best regards.
Thank you guys for your posts.
I apologize for the confusion. I try to clarify, here is the introduction of the problem (or the scenario):
Boeing (not DC or MD) aircrafts are not fitted with ram air scoop at the opposite of Airbus or McDonnel Douglas aircrafts.
This ram air scoop provides alternate air if there is no engines bleed air or the pack valveS (I mean ALL the flow control valveS) are faulty. I supposed 2 separate scenarios: all engineS flame-out caused by fuel depletion and all engineS flame-out without fuel depletion. All engineS flame-out occured at high altitude (cruise altitude). The all engines flame-out will provoke a gradual loss of pressurization (depending of the air leakage) because there is no engines bleed air. So here, we are not talking about a rapid decompression. The all engines flame-out occured before, either with or without fuel depletion (Gimly glider B767 , Air transat A330, B747 flying through volcanic ash clouds). We suppose that all engines flame-out will occur at cruise altitude in ETOPS aircrafts with 180 or 207 minutes diversion time.
I hope things are clear now and this scenario is plausible. If so, here my questions:
-Consider we have all engines flame-out (caused by fuel depletion) on Boeing ETOPS aircrafts with 180 or 207 minutes and without ram air scoop like B 757, 767, 777): how the ventilation air (without air inlet) will be provided to the all passengers during all this long diversion time at safe altitude (10,000 or 14,000 ft) mainly on Boeing aircrafts since they are not fitted with ram air scoop? (Usually chemical generator oxygen systems produce oxygen for 12-15 minutes during descent, may be more few minutes for ETOPS aircrafts).
-Could the lack of ventilation air affect the health of passengers or provoke suffocation?
It will be very helpful if someone can post the checklist of loss of thrust on both engines or loss of pressurization (or other checklist related to the subject) to figure out how ventilation air is provided mainly in ETOPS aircrafts like 757, 767, 777 that have longer diversion time.
-Consider we have all engines flame-out at cruise altitude ( caused by fuel depletion):
What you (as pilot) will do first ? (loss of thrust on both engines or loss pf pressurization checklist?) Can you please talk about the checklist on the aircraft that you fly or your know (to don't specify the kind aircraft).
-Consider we have now all engines flame-out at cruise altitude (BUT not caused by fuel depletion) and the APU is operating:
What you (as pilot) will do first ? (loss of thrust on both engines or loss pf pressurization checklist?) Can you please talk about the checklist on the aircraft that you fly or your know (to don't specify the kind aircraft).
Feedback very appreciated, thank you in advance for your help and your patience to read this long post.
Best regards.
