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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."
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.
On a recent flight from SYD to MEL our Qantas pilot ranted on the PA about how evil the ATSB was because they wouldn't let the plane take off, because Qantas engineering accidentally put an incorrect black box into our plane. He said that Qantas maintenance made mistakes like that all the time, and that, since it wasn't a safety issue to fly without a black box, the ATSB were just being pricks.
I will never set foot on a Qantas plane ever agin.
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
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?
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.