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737 'Tailstrike' Caused By Typo On a Tablet (arstechnica.com)
An anonymous reader writes: In August of last year, a Boeing 737 operated by Qantas experienced a tailstrike while taking off — the thrust wasn't great enough for the tail to clear the runway, so it clipped the ground. The investigation into the incident (PDF) has finally been completed, and it found the cause of the accident: the co-pilot accidentally entered the wrong plane weight data into the iPad used to make calculations about the takeoff thrust. "First, when working out the plane's takeoff weight on a notepad, the captain forgot to carry the "1," resulting in an erroneous weight of 66,400kg rather than 76,400kg. Second, the co-pilot made a "transposition error" when carrying out the same calculation on the Qantas on-board performance tool (OPT)—an iPad app for calculating takeoff speed, amongst other things. "Transposition error" is an investigatory euphemism for "he accidentally hit 6 on the keyboard rather than 7." This caused the problem: "For a weight of 76,400kg and temperature of 35C, the engine thrust should've been set at 93.1 percent with a takeoff speed of 157 knots; instead, due to the errors, the thrust was set to 88.4 percent and takeoff speed was 146 knots."
I used to be a Ramp Agent at a major international shipping firm. We did weight and balance for the flights. We had several layers of redundancy for our numbers: Every container number and weight was rechecked by another Ramp Agent, and then once again at the gate to match with the load sheets. We realized if we put the numbers in wrong, that could result in loss of life (not to mention aircraft assets and cargo). We took this job very seriously. Once we turned that paperwork (now done via ACARS, supposedly), I would hate to think that the cockpit just fat fingered the numbers in on their end without having a secondary check. "Hey Captain, can we check the numbers real quick?" Probably take them 15-30 seconds at most since they'd be concerned with big picture numbers and not individual positions.
If you were me, you'd be good lookin'. - six string samurai
Is there some reason they shouldn't just use 100% thrust at takeoff and make sure the cargo being carried was less than the maximum capacity?
These engines are optimized for certain turbine speeds. By staying within the recommended ranges they reduce wear & tear and improve efficiency. In addition, max acceleration is harder on the passengers. Think of it like driving a car. Do you accelerate from every stop by pressing the gas pedal all the way to the floor or do you match how much gas you give it to the driving conditions and who and how many people are in your car?
They did both do the calculation. The pilot did the arithmetic wrong and the copilot typed in his result wrong, and the upshot was that the numbers they entered independently agreed with each other... and were both wrong.
He meant a tailwind, you ignorant git. It's the velocity of air over the wings that causes lift. A sudden tailwind will reduce lift. Not knowing this just means you still have things to learn. Mouthing off about things you don't understand makes you an ignorant git.
You shouldn't even need to calculate it - the plane can measure weight itsself. There are only three points of contact with the ground, easy to mount a strain gauge in the landing gear. It might not be precise enough, but it'll be fine for sanity checking - if the measured and calculate weights differ by more than the margin of error, plane refuses to bring the engines above taxi thrust.
Headwinds are helpful for takeoff. Tailwinds are detrimental.
"Lack of speed can be overcome. In the worst case by patience." --Znork
I'm a flight test engineer that works on large (passenger-class) aircraft. We do tests related to this issue.
It actually has a lot to do with takeoff safety, ironically enough. If you lose an engine at high power, the airplane will try to yaw (turn left or right) because the engine(s) on the other side are still producing thrust. At lower speeds, with less aerodynamic forces, the rudder is not capable of keeping the airplane in a straight line. So there's a speed called "Vmcg" - "velocity minimum control ground" - below which you MUST pull back the power on the good engines to avoid going off the side of the runway (you're going to have to stop the takeoff). There's also a speed called Vmca, the airborne minimum control speed (you will start to yaw out of control).
So with less power on all the engines, there is less asymmetry possible in the event of a failure. With reduced takeoff thrust, you don't need as much rudder at any given airspeed, so your Vmcg and Vmca are both lower.
This is important for takeoff because if you have a lot of runway available, you can use it by taking longer to accelerate (by having lower thrust). As a consequence, your risk in the event of an engine failure is reduced - you won't head off into the grass if it happens on the ground, and you'll be assured of sufficient control authority if it happens in the air.
So when an airplane manufacturer builds the "takeoff performance charts", these Vmc speeds heavily factor into the takeoff planning.
Now, in this tail strike mishap, the lower weight caused the iPad to compute TOO LOW a speed. Lifting off too slow takes more nose-up (pitch) angle; lift goes up as a linear function of pitch angle; lift has to equal weight to go flying. Because of the reduced takeoff thrust, they were already planning to use most of the runway to accelerate - which put them into a corner; they were too slow to take off at the normal pitch angle, but were out of room to stop. So they pulled up until the airplane started flying - which means they pulled up high enough that the tail hit the ground (just barely in this case).
--Brandon / Split Infinity Music
At my airline, takeoff data calculations are centralized (acquired through datalink) rather than carried onboard, but still require those variables.
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?
Add in the safety factor that a heavy aircraft is better lifting off further down the runway so that the following departures and arrivals of lighter aircraft are less likely to encounter wake turbulence. As a small plane jockey, you always want to take off or land before the point the previous heavy aircraft took off, or after the point the previous heavy aircraft landed.
I suspect, sadly, that your bias against unions is an indicator that your mind is made up already.
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?
I'm only a private pilot but you also need to take into account temperature, air pressure (QNH), headwind component, the amount of runway you have to work with as well as weight to calculate takeoff performance.
For all intensive porpoises your a bunch of rediculous loosers
...but then the stupidity of taking off at less than 100% throttle to save a little bit of fuel at the expense of increasing risk is also a pretty dumb thing to do, engineering wise.
Taking off at less than 100% throttle means reduced acceleration, which reduces stress on the airframe (and passengers). It reduces wear on the engines and - more important - reduces the risk of turbine failure. It makes the aircraft easier to control (less unbalanced thrust) if it does lose an engine immediately before or after takeoff.
So...not just to save fuel.
~Idarubicin
First of all, tail strikes on take-off are obviously the result of overrotation, but this usually happens because the pilot rotates at the wrong speed. You pull back, expecting the plane to leave the ground, but instead the plane remains on the ground while the nose keeps going up. Also, you may be running out of runway if the calculations were off, so you'll pull back regardless.
About the weight sensors: good idea, but this is aviation, where everything has to work reliably in pretty difficult environmental circumstances. Even something as simple as a proximity switch to determine whether or not the gear is down, fails from time to time. We often deal with incorrect tire pressure indications, temperature indications, etcetera. Measuring the weight of a plane with sufficient precision is quite a bit more complex than a simple tire pressure reading, so I can't see any manufacturer trusting that kind of system enough to let it determine take-off settings by itself. Maybe as an extra crosscheck for the data from the loadsheet, sure, but not as the primary source of information.
People always go "we should replace the pilots with automated systems because pilots make too many mistakes", but they have no idea how many mechanical failures we deal with as part of the routine of our job. We make mistakes, sure. But so does automation.
There's a good number of reasons for this, and they're not immediately obvious.
- Optimize fuel usage; you want to burn only as much as you need on takeoff
- Reduce engine wear as much as possible. Engine overhauls are awfully expensive for airlines.
- Don't overthrust engines in case of failure. If an engine goes out on takeoff with too much airspeed the airplane might not be able to correct yaw before running out of runway.
On small piston aircrafts, yes, you usually go full power on takeoff every time. Airlines are a very different beast though.