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

From: SPRIGGS, John J < >
Date: Wed, 18 Nov 2015 10:25:23 +0000

José beat me to it; I was writing something similar. One point I have in addition is that the person doing the pen and paper check should not be the person who used the tool to do it. When there is a discrepancy, the checker must not assume that the senior person (no doubt the one with the iPAD) is correct and that (s)he has made a mistake somewhere in the working. The two people should swap methods and do it again.


Sent: 18 November 2015 10:18
To: Klaus
Cc: <systemsafety_at_xxxxxx Subject: Re: [SystemSafety] 737 tail strike caused by typo on a tablet

>> "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.


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,

Klaus Sievers

Am 18.11.2015 um 09:01 schrieb Peter Bernard Ladkin: -----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

Deja vu all over again.

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?

Prof. Peter Bernard Ladkin, Faculty of Technology, University of Bielefeld, 33594 Bielefeld, Germany Je suis Charlie
Tel+msg +49 (0)521 880 7319<tel:%2B49%20%280%29521%20880%207319>>

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