cruise altitude

[juanca]

I was wondering if the cruise altitude the flight planner gives me is accurate?

I want to fly from Mexico to Miami, and the flight planner gives me an altitude cruise of 18,000ft. I think this is too low....if so please tell me how to calculate my altitude cruise for long international trips....

I

[C]

In its most basic form of the IFR semi-circular rule, flight levels are as follows:

From 000-179deg mag track aircraft will fly "odd" FLs, ie 270, 290, 310, 330 etc

From 180-359deg they will fly "evens", ie 280, 300 etc.

As for actual flight level, it depends on your aircraft. On most sectors they higher you fly, the more fuel efficient you will be (although of course this depends on the sector length - there's no point burning a lot of fuel in the climb to FL410 if your cruise would only then be 5 minutes long).

As with all things, it's about striking a healthy balance.

Here's a more thorough explanation of FLs, although IIRC the USA doesn't use the quadrantal rule, and transition altitude in the US is always 18000ft.

http://en.wikipedia.org/wiki/Flight_level#Quadrantal_rule

[beaky]

The flight planner gives you a safe minimum altitude to avoid terrain... you can enter a higher altitude for efficiency if you want to.

[DaveSims]

Here in the US it works like this:

VFR Aircraft
Heading 000-179 fly at odd thousands +500  (ex. 5500, 7500)
Heading 180-359 fly at even thousands +500  (ex. 4500, 6500)

IFR Aircraft
Heading 000-179 fly at odd thousands (7000, 15000)
Heading 180-359 fly at even thousands (8000, 20000)

A typical airliner will cruise between 25000-35000 depending on aircraft and distance.  There isn't a set rule on choosing an attitude, you just pick one.  However the higher you go the better fuel economy.  One other thing to consider is what the winds aloft are doing, you may have a better tailwind or less headwind at different altitudes.

[ThomasKaira]

However, do not go too high, because although fuel efficiency increases with higher altitude, you also enter what has been christianed by airline pilots the "coffin corner." The higher you go, the less of a safe airspeed window you have, and as such, determining the optimum cruise altitude requires such reasoning.

Most real-world planes have published charts to tell you the optimum cruise altitude you can fly at given your weight at the time. Modern birds also convey that information through the FMC/CDU. This initial cruise altitude is planned out well before you even step into the cockpit of the plane.

Fly high, but not too high.

[C]

Quite. Alway's operate within your aeroplane's envelope. It may mean starting low and putting in several step climbs; easy if under ATC radar control, but harder in certain other conditions.

These chaps didn't. Thankfully they only killed themselves.

The Oct. 14, 2004, crash of a Pinnacle Airlines CRJ200 during a repositioning flight was owing to "unprofessional behavior, deviation from standard operating procedures and poor airmanship" on the part of the cockpit crew, "which resulted in an inflight emergency from which they were unable to recover," the US National Transportation Safety Board stated in a report issued yesterday.

Both pilots were killed when the aircraft, which was en route from Little Rock to Minneapolis-St. Paul, crashed about 3 mi. short of the Jefferson City airport, where they were attempting a deadstick landing. There were no passengers onboard and no injuries on the ground.

During the flight the pilots took the aircraft to its maximum operating altitude of 41,000 ft. for "personal and not operational issues," NTSB said. As a result of the maneuver, both engines shut down after what the Board described as a "pilot-induced aerodynamic stall. . .and their improper reaction to the resulting inflight emergency exacerbated the situation to the point they were unable to recover the airplane." Contributing to the accident was the engine core lock condition, "which prevented at least one engine from being restarted."

NTSB recommended that the aviation industry ensure training manuals contain information on high-altitude operations of RJs and that pilots receive adequate training to demonstrate their ability to identify and execute recovery from high-altitude engine stalls.

GE, which manufactured the CF34 engines powering the aircraft, said, "Tragically, the pilots. . .put the engines into a hazardous condition for which they are not designed or tested." It added, "core lock is a known industry phenomenon and can occur with any engine if operated outside of recommended flight procedures."

[beaky]

Yes, the "coffin corner" is in fact a corner of the airplane's performance envelope, where the stall speed/cruise speed margin comes to a point.
You don't have to get all the way into that corner to get into trouble, especially if you are not prepared at all for it (like those two adventurous CRJ pilots).

[-Crossfire-]

Guys, I think the coffin corner scenario is why high performance aircraft have service ceileings.  It's so these speeds dont get to close to each other.

davysims is bang on with the cruising altitudes.  The altitude you actually pick is dependant on many things, temperature, winds, cloud coverage(icing), and your operating certificate.  In Canada, under the CARS(American is FAR's), i believe only PArt 705 operators(airline) are allowed above FL250.  Part 703 and 704 (Air Taxi and Air Commuter) are restricted to under FL250.

[beaky]

Guys, I think the coffin corner scenario is why high performance aircraft have service ceileings.  It's so these speeds dont get to close to each other.

All aircraft have a service ceiling: that is, the pressure altitude at which the aircraft will not climb more than 100 feet per minute. It usually has more to do with engine aspiration than aerodynamics.

 I think most aircraft don't quite get into the "coffin corner" until they climb above the type-specific service ceiling and start nudging the absolute ceiling, which is the highest altitude at which the aircraft can maintain level flight. It can also be considered the altitude at which the plane will not climb any further.
 That altitude is where aerodynamics can really come into play in terms of performance, especially with aircraft that normally have a high stall speed-to-cruise speed ratio-  although again, it's mostly a matter of the engine (no matter what type) not being able to maintain the proper fuel/air mix.

The "coffin corner", because it represents the intersection of two speeds (Stall and critical Mach), not an altitude and a speed, could be entered at an altitude below the published absolute ceiling, and certainly well above the service ceiling.

Which is why it's best to not play test pilot unless you are a test pilot...

[Jeph]

I know this is an older thread, but i wanted to point out that U-2's fly within 10mph (not kias) of the coffin corner when they're doing their missions  :o

[Slotback]

It's not always more economical to fly higher up. First, if the route is short you may burn too much fuel climbing. Second, I'm pretty sure if, at a given weight, you go above optimum altitude you can be burning MORE fuel than if you were lower.

www.flightaware.com

Use that site and go to 'recently used IFR routes', for a good indication of altitudes and routes that aircraft fly for given routes.