[SystemSafety] 737 tail strike caused by typo on a tablet

[José Faria]

>> "The calculation is double checked using pen and paper, and so two
dissimilar faults were necessary to invoke the failure vector."

Again and again, safety arguments include claims about human/manual
behaviour that should urgently be re-visited (not to simply say, ruled out).

You are a system operator; You have a machine that calculates a value for
you; You use it and get an answer; You go and calculate it manually "to
confirm"; How biased is you manual calculation already?

Simple and harmless personal story: I was 14 years old, doing a math test.
For one of the exercises, I was able to mentally figure out the result
(value 4), before writing down the equations. Along the writing, I made a
mistake and end up with a expression resulting in square root of 36. My
brain didn't even notice and I just wrote down that SQRT 36 equals 4 and
moved to the next exercise.
When you're in a hurry, 16 isn't "that different" form 36 when you already
"know" the result, and are not really doing the calculation.

Jose'

On Wed, Nov 18, 2015 at 10:13 AM, Klaus <klaus_sievers at web.de> wrote:

> Well, hm...
> I fly 747 since 1987. Copilot, Captain...
> Distractions have increased, procedure design hasn´t quite
> kept up with all the things going on during the last minutes
> before departure.
>
> 20 years back, the data for takeoff were calculated by hand,
> using tables, and everything was ready 15, 20 minutes before
> pushback.
>
> Today, preliminary calculations are done 15, 20 minutes
> before pushback, but then updated with the latest info of
> + or - 5 passengers, a bit of cargo - whatever. THEN, with
> sheduled time of departure coming near, then things are
> recalculated and finally transferred, manually, into the airplane
> computers .
>
> Distractions ? You better be immune to them - which no-one
> can really be.
>
> About the 737: looks like a 10 ton error to me, maybe  15 % of
> takeoff-weight. May have been contributing, but I have doubts
> it was the main reason for the tail-strike.
>
> 747s , which are much larger than 737, have been known to
> scrape the runway, yes, but then the error was more than 25%
> of takeoff weight. 2xx tons instead of 3xx tons....
>
> Solution: try to keep a calm  working athmosphere in the cockpit
> and do as much preparation as can be done : every moment counts.
> And: do the checklists, the required crosschecks.
>
> Hope that this was interesting,
>
> Best,
> Klaus Sievers
>
>
> Am 18.11.2015 um 09:01 schrieb Peter Bernard Ladkin:
>
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>> Deja vu all over again.
>> http://www.rvs.uni-bielefeld.de/publications/Papers/LadkinHESSD2009.pdf
>>
>> PBL
>>
>> On 2015-11-18 06:57 , Heath Raftery wrote:
>>
>>> This news article is likely to be of interest to the list members. A
>>> jumbo's tail struck the
>>> runway on take-off, and root cause was found to be an incorrect take-off
>>> weight entered in the
>>> thrust parameter calculator. The fact the calculator is an app running
>>> on an iPad may or may
>>> not be important to the story, but it does give it that everyday appeal.
>>>
>>> The calculation is double checked using pen and paper, and so two
>>> dissimilar faults were
>>> necessary to invoke the failure vector. Is there anything more that can
>>> reasonably be done to
>>> avoid this safety issue?
>>>
>>>
>>> http://tech.slashdot.org/story/15/11/16/174213/737-tailstrike-caused-by-typo-on-a-tablet
>>>
>>
>>
>> Prof. Peter Bernard Ladkin, Faculty of Technology, University of
>> Bielefeld, 33594 Bielefeld, Germany
>> Je suis Charlie
>> Tel+msg +49 (0)521 880 7319  www.rvs.uni-bielefeld.de
>>
>>
>>
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*José Miguel Faria*
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