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Low cruise levels

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Ive been monitoring the rw flight AAL2219 for the past few days and flying it in the sim.  Im curious as to why the pilots would choose to fly so low.  As you can see they fly most of the route at fl270.  Using asn wx the winds havent been much stronger than 60 knots and have been mostly a crosswind.  

 

 http://flightaware.com/live/flight/AAL2219/history/20141107/1455Z/KMIA/TNCM

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Ive been monitoring the rw flight AAL2219 for the past few days and flying it in the sim.  Im curious as to why the pilots would choose to fly so low.  As you can see they fly most of the route at fl270.  Using asn wx the winds havent been much stronger than 60 knots and have been mostly a crosswind.  

 

 http://flightaware.com/live/flight/AAL2219/history/20141107/1455Z/KMIA/TNCM

I can think of four reasons to fly low. I'm not sure if any apply.

 

  1. Favorable winds
  2. High true airspeed
  3. Turbulence
  4. Maintenance

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Favorable winds
High true airspeed
Turbulence
Maintenance

 

I doubt maintainance would be a factor, but your other 3 options are certainly influential in choosing flight levels. Add to that ATC restrictions, and the flight planning software taking other factors into account to give an optimum flight level. Just yesterday I did a 2 hour flight on an ATR72 and we stayed at FL180 the whole time, even though we could have easily reached FL200 or 220 if needed.

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I doubt maintainance would be a factor, but your other 3 options are certainly influential in choosing flight levels. Add to that ATC restrictions, and the flight planning software taking other factors into account to give an optimum flight level. Just yesterday I did a 2 hour flight on an ATR72 and we stayed at FL180 the whole time, even though we could have easily reached FL200 or 220 if needed.

Maintenance MELs are the least likely, but it could be a MEL which does not permit RVSM flight.

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Spin737, on 08 Nov 2014 - 10:09 AM, said:

Maintenance MELs are the least likely, but it could be a MEL which does not permit RVSM flight.

Hmm yes true. But which of those would still permit passenger operations ? GPS failure or maybe 1 of the IRU's is Tango Uniform?

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I hand-flew from Fairbanks to Seattle a few months ago. No autopilot. No autopilot = no RVSM. I flew at FL270 block FL290 just to cover my butt. Pax on board.

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Spin737, on 08 Nov 2014 - 11:39 AM, said:

I hand-flew from Fairbanks to Seattle a few months ago. No autopilot. No autopilot = no RVSM. I flew at FL270 block FL290 just to cover my butt. Pax on board.

I stand corrected. Didn't know the AP was a mel-able item. What aircraft? 737? 

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I stand corrected. Didn't know the AP was a mel-able item. What aircraft? 737?

737. Can't remember if it was an NG or a CL.

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Looking at the releases for 2219 for the last few days it looks like that flight is consistently planned at FL310.  I didn't see any MEL restrictions or weather issues that would keep the flight at 31000.  Many ATC facilities have letters of agreement regarding routes and altitudes through their airspace.  My guess is something like that is coming into play with this particular route.  I'm a domestic guy so I have not flown that route so I could not tell you for certain.

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Looking at the releases for 2219 for the last few days it looks like that flight is consistently planned at FL310.  I didn't see any MEL restrictions or weather issues that would keep the flight at 31000.  Many ATC facilities have letters of agreement regarding routes and altitudes through their airspace.  My guess is something like that is coming into play with this particular route.  I'm a domestic guy so I have not flown that route so I could not tell you for certain.

Interesting, I was thinking atc as well.  What I was trying to figure out is why many times even with the flight planned for 310, the aircraft would cruise at 310 for some time and then descend to say 270 for the rest of the flight.  Since the jet uses more fuel at those lower altitudes, without significant headwinds the only thing that would make sense to me is rough air, some kind of atc restriction since it is oceanic airspace, or an mel issue.  I would expect the air to be relatively smooth over the Caribbean on a day without strong storms as well, so that leaves atc or mel.

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Looking at the releases for 2219 for the last few days it looks like that flight is consistently planned at FL310.  I didn't see any MEL restrictions or weather issues that would keep the flight at 31000.  Many ATC facilities have letters of agreement regarding routes and altitudes through their airspace.  My guess is something like that is coming into play with this particular route.  I'm a domestic guy so I have not flown that route so I could not tell you for certain.

 

This was one of my first thoughts as well. I don't have any connections down there to answer any questions for me, though. I might in a few weeks, though.

 

An example up here would be DC-NY, which is routinely kept at 17,000 - FL210, depending on the airport in N90.

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Today's flight, now about 1+43 enroute, is at FL380 as filed.  Go figure. I was waiting for Kyle to chime in because I'm not as current in airspace structure as he seems to be. As mentioned, I am aware of the US NE routes held low for lots of cross traffic and we even have a few spots here in Texas where the enroute ceiling is limited by ATC (even Texas gets smaller at jet speeds, unless you cross the entire state lol).  The route is within Class II so my guess would be that a temporary restriction due to whatever, like rocket launch, were in effect.

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Go figure. I was waiting for Kyle to chime in because I'm not as current in airspace structure as he seems to be.

 

Airspace intricacies are actually pretty unique to each area. There are even some spots of Washington Center that I don't quite understand, but I also have a few contacts that I can text to have an answer within a few hours. MIA, MIA Oceanic and ZNY Oceanic are neither specialties of mine, nor do I have contacts, unfortunately. Well...apart from VATSIM, but I'm always hesitant to use them in RW scenarios because, despite a lot of them using RW SOPs, corners are cut to make it more VATSIM-friendly in many cases.

 

Still - much of the Oceanic areas (US or otherwise) are mostly non-radar, which always adds extra odd procedures/layers into the mix. I doubt that it has too much to do with it, but I do know that facilities have all kinds of LOAs, which are "off the books" to a certain degree (you could get them via FOIA as a citizen - they're just not evident via maps/charts/etc is what I'm getting at).

 

My buddy at one of the centers was saying that pilots have been requesting extraordinarily low cruising altitudes because of turbulence, so that could be most of it. I wouldn't be surprised at all.

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The flight that flew today was at FL370, so not airspace restrictions.

They only filed at 310 from 11/8-11/11.  Before that time, they were at 370...same with after

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They only filed at 310 from 11/8-11/11.  Before that time, they were at 370...same with after

 

My money would be on turbulence then. My controller buddies working the lower sectors said they were getting slammed all over the East Coast because of turb higher up, keeping crews lower. Happy passengers means more return passengers...

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My money would be on turbulence then. My controller buddies working the lower sectors said they were getting slammed all over the East Coast because of turb higher up, keeping crews lower. Happy passengers means more return passengers...

 

That would normally have been my guess as well but having looked at the releases for the flights in question I didn't see anything in the turbulence forecast along the route.  Typically the dispatcher will put something in the remarks section when they file us at an unusual altitude or route to indicate why they did so.  There were no remarks on any of the releases in question.  It's very possible the captain and dispatcher discussed the issue by phone prior to dispatch which would explain the lack of remarks.

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