77 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 ...
DeltaLima's user avatar
  • 83.4k
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, ...
GdD's user avatar
  • 54k
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 ...
Peter Kämpf's user avatar
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 ...
randomhead's user avatar
  • 15.2k
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. ...
Gerry's user avatar
  • 19.8k
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 ...
John K's user avatar
  • 131k
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 ...
vasin1987's user avatar
  • 8,128
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 ...
Peter Kämpf's user avatar
27 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 ...
John K's user avatar
  • 131k
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,...
kevin's user avatar
  • 39.7k
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 ...
pcfreakxx's user avatar
  • 1,988
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 ...
niels nielsen's user avatar
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 ...
StephenS's user avatar
  • 27.7k
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 ...
U_flow's user avatar
  • 3,655
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 ...
Dave's user avatar
  • 101k
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 ...
quiet flyer's user avatar
  • 22.6k
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 ...
FreeMan's user avatar
  • 16.2k
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 ...
Peter Kämpf's user avatar
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....
Noah Krasser's user avatar
  • 8,992
12 votes
Accepted

Will control surfaces on a plane be less efficient at a higher altitude?

Please let me assume that you wonder about control surface effectiveness rather than their efficiency. Both are closely related, but I prefer to address their effectiveness - doing what the pilot ...
Peter Kämpf's user avatar
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 ...
GdD's user avatar
  • 54k
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 ...
Jpe61's user avatar
  • 28.8k
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 ...
Bianfable's user avatar
  • 55.9k
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 ...
HiddenWindshield's user avatar
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 ...
quiet flyer's user avatar
  • 22.6k

Only top scored, non community-wiki answers of a minimum length are eligible