United Overweight Takeoff on Computer Mistake Prompts Changes
According to this report, incorrect information provided by dispatchers to the flight crew with caused this UAL 737-900 to take off at a weight about 20,000 pounds (9,071 kilograms) heavier than than pilots believed.
United sent pilots a weight estimate that assumed the coach section of the Boeing Co. (BA) 737-900 was empty when it was full. ... While the pilots, who didn’t catch the mistake, had difficulty getting the jetliner airborne, the plane wasn’t damaged and the flight was completed without incident. ... Boeing’s 737-900 models can take off weighing as much as 187,700 pounds (85,141 kilograms), according to Boeing’s website.
Given that the pilots obviously knew how much fuel they were carrying, and that they had a full load of passengers, it seems concerning that they didn't notice such an anomalous figure for total weight. Note that this instance seems different from the Emirates MEL flight where an incorrect weight was inadvertently keystroked into the FMS. Here the provided weight sheet was wrong.
Seems like we may be back to discussing the possibility of implementing a line check speed, as when Emirates took a tour of the departure end in Oz a while back. Every military fighter I ever flew had a line check speed. The number was calculated for each flight before anybody ever headed toward his aircraft. Infallible system. Sir Isaac Newton: Force=Mass times Acceleration. After brake release, you looked at your ASI as you passed the 1000-foot mark (2000 feet for some aircraft) on takeoff roll. If you didn't achieve that number, you aborted. Figured out what was wrong. Lived to fly another day. Didn't run off the end of the runway dragging a bunch of navaid equipment with you. If you were off by 3-4 knots, that was ok. Off by 5 or more knots, abort. If the Force (thrust) was inadequate or the Mass was too great, not enough Acceleration was produced, making you "check speed" too slow. Simple, effective. No laptop or dispatch needed.
Our 747 freighters had a weight readout but, whilst the B744 was OK, the old B747 system was considered too expensive to maintain and was disconnected.
the possibility of implementing a line check speed
I understand the V Force used that system. I wonder if it would be workable with the civil airline complication of variable thrust? Whilst I guess the speed could be tabulated or otherwise calculated would errors result in unnecessary aborts?
I have been very interested in performance for many years, T/O and LDNG performance is so interesting.
We have seen so many examples of getting it wrong on T/O and LDNG, I guess many many get un-reported to a greater or lesser extent.
I used to think an easy "rule of thumb" chart could be used to help/assist in helping/informing/assisting to avoid falling into traps, I guess it can be of help, but history records it has limited use/effect.
I list a a few examples of classic events that may of been helped/avoided if a system was in place to remove/reduce/reduce-effect them, see below.
Air Florida, EK at MEL, SQ at AKL etc etc.
As the previous and so many un-mentioned events show that operating pilots can't see the big picture of performance/power/thrust/EPR/N1/availabe runway lenght/distance avail etc etc.
So many systems avail to help assist this prob, but cure could be less safe overall.
Reminds me of also runways not in use and reduced runways problems.
the possibility of implementing a line check speed
There is a simpler way which is easily automated. What really matters is acceleration which is easily measured and runway length which is a simple database item. We do not need to rely on weight or thrust calculations which are error prone. If the acceleration is not enough to achieve a safe accelerate/V1/stop distance within the available runway length just sound an ABORT ABORT alarm.
Last edited by The Ancient Geek; 13th Aug 2012 at 23:31.
There's a bit of a complication to that accelerometer-based approach in a potentially gusty wind; but, it should be able to spot when either the mass is significantly higher than assumed, or the thrust is less.
You'd need to wait until power has stabilized too, but with both GPS and inertial navigation giving acceleration, there should be no doubt about whether Mr Newton recommends it'll be time to go flying before hitting the lighting boom.
A half decent programmer can write a calculation program that asks pertinent questions to error check the fuel/TO calcs.
In the case of EK, a simple series of questions, like departure location, destination, aircraft type (for the AB guys who swap a lot), POB, windspeed would come back with an answer that can be compared with the crew calcs.
A simple result of 'very near' or 'miles out' would be returned.
As a non-pilot I don't pretend that I've ever used it but as a former load controller I seized the opportunity to acquire a piece of technology that failed to replace me! I'm told the acronym means Sum Total And Nosewheel.
I'll leave it to an expert to explain how it worked.