Needing Descent Due "Altitude Restrictions"
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Needing Descent Due "Altitude Restrictions"
Hi all, I'm an ATCO after some info following a request that was unusual and not really understood by us.
A B767-300 called on frequency descending FL350. Due to other traffic I gave a Mach restriction of M0.74. The pilot then said "London, we need descent" and I gathered from the tone that it wasn't just a "request descent" but something a little more important. I said that due to 2 other aircraft it'll take a few minutes unless there was a problem, and got the response "we need to go down now due to a technical reason". The other 2 aircraft were swiftly vectored and 20 seconds later I issued descent to the B767. The frequency got a little busy for a few minutes and after it calmed, I asked the B767 if there would be any problems in completing a normal approach, the response was "negative, we just had an altitude restriction problem, but everything is fine now" and a "thanks very much for that help" on transfer.
So my question basically is can anyone explain what this might have been in a non-technical speak so I can understand the problem? Also could it simply have been my Mach restriction causing the problem (I could quite happily have given a "when able" but thought at FL350 M0.74 would have been possible on a B767)?
Cheers in advance
5mb, confused ATCO
A B767-300 called on frequency descending FL350. Due to other traffic I gave a Mach restriction of M0.74. The pilot then said "London, we need descent" and I gathered from the tone that it wasn't just a "request descent" but something a little more important. I said that due to 2 other aircraft it'll take a few minutes unless there was a problem, and got the response "we need to go down now due to a technical reason". The other 2 aircraft were swiftly vectored and 20 seconds later I issued descent to the B767. The frequency got a little busy for a few minutes and after it calmed, I asked the B767 if there would be any problems in completing a normal approach, the response was "negative, we just had an altitude restriction problem, but everything is fine now" and a "thanks very much for that help" on transfer.
So my question basically is can anyone explain what this might have been in a non-technical speak so I can understand the problem? Also could it simply have been my Mach restriction causing the problem (I could quite happily have given a "when able" but thought at FL350 M0.74 would have been possible on a B767)?
Cheers in advance
5mb, confused ATCO
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Loss of one pack is restricted to FL 350. That's our MEL restriction. There's a possiblity that a pack loss was behind the request for FL 350.
However, MEL's are for dispatch requirements and you'll get opinions all over the map if the a/c has to descend to FL350 if it losses a pack after departure.
I've been at FL 390 and lost a pack. Stayed at FL 390. FL 350 restriction (MEL) was for departure and we were already flying.
Matter of fact, we were overwater and it was much easier to stay at FL390 vs. declaring emergency, etc, etc. to descend for a 'non-issue'. If we couldn't maintain pressurization obviously we would have had to descend.
However, MEL's are for dispatch requirements and you'll get opinions all over the map if the a/c has to descend to FL350 if it losses a pack after departure.
I've been at FL 390 and lost a pack. Stayed at FL 390. FL 350 restriction (MEL) was for departure and we were already flying.
Matter of fact, we were overwater and it was much easier to stay at FL390 vs. declaring emergency, etc, etc. to descend for a 'non-issue'. If we couldn't maintain pressurization obviously we would have had to descend.
G'day 5mb,
Just to clarify things was the B767 descending from FL350 or descending to FL350 when the request was made? What final level did the aircraft require and end eventually up at?
Regards,
BH.
Just to clarify things was the B767 descending from FL350 or descending to FL350 when the request was made? What final level did the aircraft require and end eventually up at?
Regards,
BH.
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Losing a pack I could understand but feel it may have been something different.
The aircraft checked in on frequency descending to FL350 as per the norm for that routing and levelled for about 30 seconds before then requesting further. It was on a normal descent profile to begin approach and land. Due to the wind most inbounds on that routing wanted earlier descents to hit level restrictions further down the line but the pilot gave another reason that was unexpected.
The aircraft checked in on frequency descending to FL350 as per the norm for that routing and levelled for about 30 seconds before then requesting further. It was on a normal descent profile to begin approach and land. Due to the wind most inbounds on that routing wanted earlier descents to hit level restrictions further down the line but the pilot gave another reason that was unexpected.
G'day 5mb,
The loss of one pack wouldn't cause pressurisation problems unless there were further complications. Even with both packs INOP the aeroplane won't depressurise instantly, quickly but not instantly.
On re-reading your first post and this bit in particular
it sounds like he thought there was going to be a problem meeting an altitude requirement further down the descent as alluded to in your subsequent post
Maybe the phrasing he used was a little unusual.
Personally I wouldn't have thought a profile problem at FL350 would be that urgent.
Regards,
BH.
The loss of one pack wouldn't cause pressurisation problems unless there were further complications. Even with both packs INOP the aeroplane won't depressurise instantly, quickly but not instantly.
On re-reading your first post and this bit in particular
"negative, we just had an altitude restriction problem, but everything is fine now"
most inbounds on that routing wanted earlier descents.
Personally I wouldn't have thought a profile problem at FL350 would be that urgent.
Regards,
BH.
Last edited by Bullethead; 16th Jun 2009 at 08:40.
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Cheers BH. I did have a couple of RTF exchanges explaining briefly the traffic situation and the polite but short reply was they wanted descent immediately due to something technical. I almost expected to see the Mode C start moving prematurely for something like a depressurisation and the other two aircraft were given some harsh headings to get them well out of the way and my planner was on the phone letting the two abutting sectors know why some of my traffic is steaming their way. Both me and my planner were expecting some sort of emergency from the unusual replies and just cannot think of what the problem was. It was an english pilot flying for one of our regulars on a normal route and further on down the descent I imposed a 270kt restriction which caused no problems for hitting the standing agreement level - the aircraft was actually 3000' lower at the point!
We have a nose for something thats not quite right, more often than not I can tell when someone is about to ask for something out of the ordinary or ask for some sort of special handling (medical emergencies etc), the voice just has that slight change of tone, I'm sure pilots occasionally can hear it in a controllers voice every now and then too. Its just a pain in the arse when we actually have no idea what the problem was and if we gave the best possible service or not, or whether the 45 deg changes to the other traffic was really necessary, the 3 other aircraft in other sectors really needed moving off route, and if the subsequent screwy presentation as a result to the next sector was totally unavoidable. There was too much else going on yesterday afternoon to actually ask why, hence me coming on here to see if anyone can assist.
Cheers
We have a nose for something thats not quite right, more often than not I can tell when someone is about to ask for something out of the ordinary or ask for some sort of special handling (medical emergencies etc), the voice just has that slight change of tone, I'm sure pilots occasionally can hear it in a controllers voice every now and then too. Its just a pain in the arse when we actually have no idea what the problem was and if we gave the best possible service or not, or whether the 45 deg changes to the other traffic was really necessary, the 3 other aircraft in other sectors really needed moving off route, and if the subsequent screwy presentation as a result to the next sector was totally unavoidable. There was too much else going on yesterday afternoon to actually ask why, hence me coming on here to see if anyone can assist.
Cheers
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Mach .74 seems unusually slow for a 767 at FL 350, and equates to not much drag. Couple that with a tailwind, and even with engines back at idle it probably glides just too well to meet expected descent altitude restrictions.
I suspect the pilot just did not want to use speedbrakes. Creates a slight rumble in the cabin.
I suspect the pilot just did not want to use speedbrakes. Creates a slight rumble in the cabin.
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Ok, to push the slow speed against descent profile out of the way, what is the average min clean speed for a B767-300ER at FL350 beginning final descent after cruising at FL380 on a 5 hour flight bucket and spader (charter to those that may not get that!)? I'm assuming we are close the the back of the envelope but thought it would be just possible, or a call saying "can't do that just now" would be made.
If the speed restriction was compromising the level restriction expected then normally we just get "can't slow and make the level, what would you prefer". Also having given 270kts for IAS and the aircraft easily complied makes me think that this wasn't the problem.
As I said, the tone of voice just wasn't quite right for a profile to hit the gates problem.
If the speed restriction was compromising the level restriction expected then normally we just get "can't slow and make the level, what would you prefer". Also having given 270kts for IAS and the aircraft easily complied makes me think that this wasn't the problem.
As I said, the tone of voice just wasn't quite right for a profile to hit the gates problem.
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Not an airline pilot but 270 kias should certainly be acceptable to a 767. If he's heavy, or has engines spooled up for anti ice, or has a tailwind, and needs to make an altitude restriction then that's what speed brakes are for. But a charter on return should be light, so I'm guessing .74 would be acceptable as min clean at FL350.
I'm guessing that's about 220 kcas, slower than they'd prefer, as you say don't want to get backside of the thrust required curve. May end up pushing the throttles both ways trying to maintain that speed.
I'm guessing that's about 220 kcas, slower than they'd prefer, as you say don't want to get backside of the thrust required curve. May end up pushing the throttles both ways trying to maintain that speed.
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Funfly, didn't even have time for that yesterday, I was enroute holding for Heathrow in the sector at the time, and watching with amazement at the carnage of weather avoiding in the sector next to me, as well as trying to stay well out of their way. It was not a very well timed problem!
