Depressurization Escape Routes

[RedTailSwinger]

I've heard airlines create depressurization escape routes over mountainous terrain. How can a pilot legally descend below the MEA to comply with an airplanes rapid depressurization profile?

For example, the depressurization profile for the A320 is a descent to 18K within the first 5 minutes. Then after an additional 7 minutes (12 minutes from start) you must begin a descent to 14K. Then after an additional 30 minutes (42 minutes from start) you must be at 10K. The MEAs for many routes in the world are over 20 thousand feet.

Also, I've heard airlines create escape routes for Bogota. Why is this necessary when the normal routes of flight are over a valley?

 

[i'mbatman]

Well those resons are why their are escape routes.....you really only go as low as you can, I mean if you need to go to 10000 for a depress but there are mountains at 14000, what are you going to do? If airlines publish escape charts and they are approved as part of their SOP's, the MEA's on them are valid.....i think that answers your q. I can't answer your question regarding bogota but in China(himilayas) and up near ANC(rockies) there are escape routes.

 

[regionalcap]

I've heard airlines create depressurization escape routes over mountainous terrain. How can a pilot legally descend below the MEA to comply with an airplanes rapid depressurization profile?

For example, the depressurization profile for the A320 is a descent to 18K within the first 5 minutes. Then after an additional 7 minutes (12 minutes from start) you must begin a descent to 14K. Then after an additional 30 minutes (42 minutes from start) you must be at 10K. The MEAs for many routes in the world are over 20 thousand feet.

Also, I've heard airlines create escape routes for Bogota. Why is this necessary when the normal routes of flight are over a valley?

The MEA is for a particular airway. If you change your route (follow the critical terrain route), then you have a new lower altitude.

 

[Spooky 2]

Suplemental O2 for D/D

Airlines who operate over extremely high terrain have created escape routes for their individual aircraft assigned to those particular ops. Most airlines have these depicted on their "tailored" Jepp charts. Some escape routes that do not allow for a rapid descent below say 14,000, or in most cases 10,000' and require additional oxygen be put onboard for a certain percentage of the passenger capacity and thus require "supplemental oxygen". On the other hand some operators have opted for the chemical canisters that provide something greater than 15 minutes. I think there is a 20' option and perhaps a 30 miniute option available on some Boeing aircraft. In lieu of that you can equip a B777 with a totally gaseous system and delete the oxygen canisters all together. The point is that there are many different ways to skin a cat and how your operation handles it, may look a lot different than the other guys. The Hindu Cush operation from Europe to India would be a good example of an extreme case where the additional oxygen would be reuired. Also many routings over Greenland will not allow for a timely descent and thus requires some sort of additional oxygen. When required and the aircraft is not equipped with a built in solution, airlines typically put extra O2 bottles in the overhead compartments with masks attached. Kind of a band-aid appoach IMO, but it meets the letter of 121 regs.

Hope that helps...Spooky

 

[pianoman]

On our EWR-India routes we take an extra oxygen cart with us. As you said, it meets the letter of the law but perhaps not the spirit.

 

[Beetle007]

On our EWR-India routes we take an extra oxygen cart with us. As you said, it meets the letter of the law but perhaps not the spirit.

What does Continental use on their South American routes over the Andes?

 

[Spooky 2]

What does Continental use on their South American routes over the Andes?

I'm pretty sure you will find that they use the same concept as used in the EWR to India routes as this is proably the most common methodology in practice today. CAL pitch in here if I'm wrong.

 

[AC560]

How can a pilot legally descend below the MEA to comply with an airplanes rapid depressurization profile?

I would think 91.3(b) would be all the cover you need from the legal aspect of the question.

 

[Spooky 2]

I would think 91.3(b) would be all the cover you need from the legal aspect of the question.

NO, NO....no one is suggestig that it is okay to descend below the MEA for a given area. That's why these special routingings have "escape routes" that minimize the time you need to remain above the MEA and that's also the reason that you have supplemental oxygen onboard. No one is supposed to descend below an MEA and if you read something into this as a approval for that, you are wrong.

 

[macdu]

Moca, Mva

 

[Beetle007]

Ive been told there are times you must go below the MEA to follow the aircraft's depressurization profile.

 

[pianoman]

Ummm... unless I have a chart in front of me specifying a lower altitude I'm not going below MEA. The pax can survive a little while at 15k- no one will survive the mountain we hit.

 

[acbarney]

What does Continental use on their South American routes over the Andes?

We have escape routes in our jeps for bogota, quito, lima and a few others.

 

[Spooky 2]

Ive been told there are times you must go below the MEA to follow the aircraft's depressurization profile.

Where did you hear or read that? So what did this say, yea go down to the MOCA or?? I don't have access to any charts where I'm at but basically this is a matter of whether you continue along your flight planned route, deviate so as to use the escape routing and altitudes, turn around a go back the way you came in, which ever is the better.

There is so much more to this than meets the eye and frankly I don't consider myself anything of an expert on this aspect of flight planning as this is why God made dispathers in the 121 world.

Driftdown is different for each airframe and engine combination and in some cases there are more than one speed for the same aircraft. Extreme examples of this are the early series -1, L1011 where in some cases with the loss of two engines, you actually have to dump fuel to keep from splashing in the ocean. Obviously with this scenario, any terrain is to much and the airplane would have to be flight planned or loaded in such a manner to avoid this potential disaster. Of course 2EO on a three engine aircarft is highly unlikely. For two engine ETOPS aircarft the critical engine failure includes a catastrophic engine failure combined with a pressurization loss thus requiring the aircarft to get below 10K so as to have enough oxygen for the pax and crew. This has been covered in previous posts here under this subject. So obviously terrain is the killer item in these situations. I'm sure there are a host of places in this world that cause significant flight planning issues depending on height of the terrain, gross weight of the aircraft and OAT/wind along the flight path.

Your responsibilty as a crew member is to know the exact procedures for your particular aircarft. Most if not all follow a similar course of action in that you need to set MCT on the good engine, let the aircraft slow to some FMS designated DD speed, usually something like max lift over drag. Set the desired altitude the MCP decide which way you will turn for terrain or traffic considerations or a specified offset in oceanic airspace and start down. I would be very hesitant to descend below an MEA unless I could maintain visual contact with the surrounding terrain and even then there is no guarantee that you would not box yourself in someplace and wind up another mountain statistic.

 

[typhoonpilot]

I deal with depressurization strategies quite often. These are routings that are researched and have terrain clearance based on being within 5 miles of the airway/direct routing given. They do go below the MEA for many airways that we are on, but MEAs are not just for terrain so I don't see the big hang-up on going below the MEA. They also go below the Grid MORA. Again, these are researched routings and guarantee terrain clearance on an average day.

The important thing about them is that they are a regulatory requirement as previously mentioned. They are designed to get you down to a legal altitude in the time required based on the oxygen you have on-board. For us that means getting down to 14,000 feet in roughly 20 minutes ( the time our oxygen generators last for ). Then getting down to 10,000 feet some time therafter based on our intepretation of this regulation: "A supply of oxygen for 10% of the passengers for the entire flight time when the cabin pressure altitude exceeds 10,000 feet, but does not exceed 14,000 feet, after the first 30 minutes at these altitudes."

We are told that the altitudes take into account the average temperature and QNH on those routing, but to be careful my strategy in these is this: If it says descend to 14,000 I will first decend to 17,000 while checking the area QNH and temperature. I will then make adjustments based on the differences from a standard day and descend to 14,000 true altitude or 14,000 feet indicated altitude, whichever is higher. Over Greenland in the winter you could have a significant difference between true altitude and indicated altitude based on below standard outside air temperatures.


Typhoonpilot

 

[AC560]

No one is supposed to descend below an MEA and if you read something into this as a approval for that, you are wrong.

Original question "How can a pilot legally descend below the MEA to comply with an airplanes rapid depressurization profile?".

What is wrong in my answer. Nobody is supposed to land a plane in the middle of a freeway either, given the appropriate circumstances though one does what one must. The legal clearance that the poster is looking for is 91.3 (b). Whether that decision is wise or not is an entirely different subject.

 

[SuperFLUF]

....How can a pilot legally descend below the MEA to comply with an airplanes rapid depressurization profile? ......

Captain's emergency authority.

 

[pianoman]

I understand the question, but really who cares about the airplane's pressurization schedule if you aren't sure where the terrain is?

The plane will fly fine unpressurized. Maybe the pax take a nap for a bit.

 

[Beetle007]

I understand the question, but really who cares about the airplane's pressurization schedule if you aren't sure where the terrain is?

The plane will fly fine unpressurized. Maybe the pax take a nap for a bit.

I think this issue matters from a flight planning standpoint. As a pilot you must be capable of following the depressurization profile of the aircraft and therefore must know the location of terrain and how low you can descend.

Or, imagine an FAA line check when they ask you "What would you do if you had a rapid decompression right now?"

Things are always easier from a practical standpoint (i.e., emergency authority) than from a regulatory standpoint.

 

[SuperFLUF]

I understand the question, but really who cares about the airplane's pressurization schedule if you aren't sure where the terrain is?

The plane will fly fine unpressurized. Maybe the pax take a nap for a bit.

How long will your crew O2 last? At what altitude? Was your O2 bottle serviced full before you took off or just within limits? It gets awfully cold up there...etc.

What if an engine fails and the engine inop altitude is below the terrain? Better have a plan on where to go before you're dealing with an engine out. Especially if its accompanied by control issues or a fire.

If you've got the low alt charts on board, in most cases that's all you need to find an airway that will get you down and headed to a diversion airport.