78
votes
Accepted
How can an altimetry system error during cruise (500 ft at 35000 ft high) cause an insufficient fuel situation?
If the aircraft is cruising at FL350 it is operating in Reduced Vertical Separation Minima (RVSM) airspace (between FL290 and FL410).
With an altimetry discrepancy between the two altimeters of more ...
- 83.8k
43
votes
Why are heavy flaps better than just a bigger wing?
When flaps are retracted they do nothing, which is the whole point. The byproduct of lift is drag, a larger wing will create more lift, but more drag as well. More drag equals a slower cruising speed, ...
- 54.1k
39
votes
Why do missiles typically have cylindrical fuselage and not a fuselage that generates more lift?
Rockets with solid fuel must be round, or they would weigh more. Remember that the rear part is filled with fuel which gradually burns away, so the whole fuel container has to withstand the pressure ...
- 236k
36
votes
Accepted
Why are planes required to cruise at round flight levels only above 18000 ft of altitude?
In general, the minimum vertical distance two IFR aircraft can be (if they are not separated laterally) is 1,000 feet. This allows for inaccuracies, for example due to:
altimeter error
...
- 16.3k
34
votes
Does flying slower actually save fuel?
Yes it saves fuel, unless you get really slow (well below cruise speed - more later.)
Since drag (and thus power required) increases with the square of velocity it will save fuel for the total flight. ...
- 20.1k
28
votes
Accepted
How do planes maintain constant speeds at cruise altitudes?
The autopilot pitches to hold the flight level when it captures the level at the top of the climb, so later on as the aircraft gets lighter and wants to climb further, the A/P will lower the nose as ...
- 134k
28
votes
Accepted
Do airliners reduce their angle of attack to maintain lift = weight as fuel burns off during cruise?
Yes. As fuel is burned the airplane will want to climb, so the autopilot (which is flying the plane 99% of the time and will normally be in altitude hold mode once you're at your clearance Flight ...
- 134k
27
votes
Why cruise at 7000' in an A319?
The only reason for your flight to operate at such low altitude is because it is cheaper for them to do so.
As you said it is due to weather, other route/altitude may not be available. They can ...
- 8,160
27
votes
Accepted
Why are heavy flaps better than just a bigger wing?
Your concerns about heavy flaps are well founded. The designers try to get away with as few high-lift devices as they can afford to. But not fewer!
If you observe the trend over the years, flaps ...
- 236k
26
votes
Accepted
How much leverage do commerial pilots have on cruise speed?
There is something called the "Cost Index" - it is basically how you choose between speed and fuel economy. Company dispatchers, after knowing that a flight has been delayed, will calculate this value,...
- 39.8k
24
votes
How do planes know what altitude they're cruising at?
Above Transition Altitude (e.g. this is 5000ft in Germany) the altitude is measured in flight levels (FL) - each FL equals 100ft and is measured above an artificial QNH of 1013,25 hPa.
If you cruise ...
- 1,978
20
votes
Do airliners reduce their angle of attack to maintain lift = weight as fuel burns off during cruise?
It's almost always more economical to fly higher if you can. So, as an airliner burns off its fuel load, it will naturally want to climb higher, and the pilot will request clearance to do so in stages ...
- 22.1k
16
votes
Accepted
Why cruise at 7000' in an A319?
It was because they could get there faster on a "TEC route."
IFR flights are subject to congestion management at the ARTCC level, which means they have to wait their turn in line to be allowed into ...
- 27.8k
16
votes
Why do missiles typically have cylindrical fuselage and not a fuselage that generates more lift?
There are several reasons why most missiles have a round shape. I try to list (some of them) in roughly ascending order of importance:
Round shapes with wings are easy to calculate: Well known rough ...
- 4,891
14
votes
Accepted
What is a Cruise Captain?
According to the discussion here it seems a "cruise captain" is the captain who flies only during the cruise stage of flight. You can find a job listing for a "cruise captain" here but it does not ...
- 102k
14
votes
Why are planes required to cruise at round flight levels only above 18000 ft of altitude?
This answer is specifically for the US--
Above 3000' AGL and below 18000' MSL (which is not the same thing as FL 180)1, cruising VFR traffic flies at MSL altitudes which are "round" numbers ...
- 23k
13
votes
Why are heavy flaps better than just a bigger wing?
Climb to cruise burns fuel.
Adding additional drag burns fuel.
Adding retractable mechanisms adds weight that burns fuel.
More drag, even at higher cruise altitudes, requires larger engines for the ...
- 16.4k
13
votes
Based on this fuel flow chart, why isn't it more optimum to remain at an intermediate altitude rather than climbing?
When airplane mass, altitude, N1 (engine spool speed) and Mach number change together, it is very hard to come to a meaningful conclusion what is better for fuel flow. However, you see that the grey ...
- 236k
12
votes
Why would a plane drop 14.000 ft mid flight?
I looked up the flight on Flightradar24.com. The descent starts at 16:10 UTC and ends at 16:29 UTC, going from 38.000 feet to 24.000 feet. So, the aircraft descended 14.000 feet in 19 minutes.
14....
- 9,002
12
votes
Accepted
Do pilots keep light in the cockpit during long night flights?
White lights are usually off in the cockpit in night flights to protect pilots' night vision. Red lights are sometimes used as these do not impact night vision.
One of the challenges you'll run into ...
- 54.1k
11
votes
Do pilots keep light in the cockpit during long night flights?
If you are asking about logging night VFR -time, you are not concerned with lighting conditions. Night time is logged according to regulation based definition of night (at least EASA), tables for ...
- 30k
11
votes
Accepted
How is the Dash 8 Q400 so fast?
Here are the cruise performance tables for the Q400 at the heaviest and lightest weight (click to view larger):
Source: from the Dash-8 Q400 performance manual, which came included with a simulator ...
- 57.6k
10
votes
Accepted
How do planes know what altitude they're cruising at?
To combine the other two answers:
Below the "transition altitude" (which is 18,000 feet in the US, 5,000 feet in Germany), the pilot has to pay attention to the current altimeter setting, and adjust ...
- 12.8k
10
votes
Why are heavy flaps better than just a bigger wing?
The questioner seems to have noted that the basic wing with flaps retracted provides a high ratio of L/D (or Cl/Cd). Where L denotes lift, Cl denotes lift coefficient, D denotes drag, etc.
We can ...
- 23k
9
votes
What is a Cruise Captain?
On long haul flights that require additional crew members, airlines use various ways to meet the regulatory or contract requirements.
Many airlines add just additional First Officers (co-pilots). For ...
- 37.9k
Only top scored, non community-wiki answers of a minimum length are eligible