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

Wed Nov 18 20:44:27 CET 2015

Interesting discussion and one which exemplifies the Efficiency 
Thoroughness Trade Off (ETTO) which exists.

The most thorough (and safe?) way would be to have two pilots to do two 
individual calculations using different media (both electronic but 
different algorithms, or manual and electronic) and then do the same in 
the other medium, then cross compare to ensure that the answers are the 
same. If not, go back in and try to work out where the error was. This 
would have been the only way to trap the error from this incident due to 
the same answers but different modes of failure 
(http://atsb.gov.au/media/5727742/ao-2014-162_final.pdf). This has a 
time implication as highlighted by Klaus below.

However, in the real world, time is a real driver with many low cost 
airlines only at the gate for 30-60mins before leaving again and given 
the massive number of take-offs and landings taking place with similar 
process, and the lack of accidents, the airlines are making a calculated 
risk that the current methodology is acceptable. The regulators must 
also think this is the case too.

Despite all of the calculations being correct, you can have issues with 
crew taxing to the incorrect part of the runway, being convinced that 
they are at the end of the runway because of the visual cues present, 
turn around and take-off some 2000ft further into the runway than they 
thought...as they passed the upwind threshold thinking that was quicker 
than thought and then looking on Google Maps to see that the taxi chart 
didn't quite represent the real world...!! An incident report was filed 
by the crew so others could learn from their mishap.

Regards

Gareth Lock
Managing Director
Human in the System Consulting

M: +44 7966 483832
E: gareth at humaninthesystem.co.uk
W: http://www.humaninthesystem.co.uk
T: @HumaninSystem <https://twitter.com/HumaninSystem>

Skype: gloc_1002
WhatsApp: +44 7966 483832

This email and any files transmitted with it are confidential and 
intended solely for the use of the individual or entity to whom they are 
addressed. If you have received this email in error please notify the 
sender by email or telephone. This message contains confidential 
information and is intended only for the individual named. If you are 
not the named addressee you should not disseminate, distribute or copy 
this e-mail. Please notify the sender immediately by e-mail if you have 
received this e-mail by mistake and delete this e-mail from your system. 
If you are not the intended recipient you are notified that disclosing, 
copying, distributing or taking any action in reliance on the contents 
of this information is strictly prohibited.

> SPRIGGS, John J <mailto:John.SPRIGGS at nats.co.uk>
> 18 November 2015 at 10:25via Postbox 
> <https://www.postbox-inc.com/?utm_source=email&utm_medium=sumlink&utm_campaign=reach>
>
> 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.
>
> John
>
> *From:*systemsafety-bounces at lists.techfak.uni-bielefeld.de 
> [mailto:systemsafety-bounces at lists.techfak.uni-bielefeld.de] *On 
> Behalf Of *José Faria
> *Sent:* 18 November 2015 10:18
> *To:* Klaus
> *Cc:* <systemsafety at lists.techfak.uni-bielefeld.de>
> *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.
>
> Jose'
>
> On Wed, Nov 18, 2015 at 10:13 AM, Klaus <klaus_sievers at web.de 
> <mailto: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:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA256
>
> 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 <tel:%2B49%20%280%29521%20880%207319> 
> www.rvs.uni-bielefeld.de <http://www.rvs.uni-bielefeld.de>
>
>
>
>
> -----BEGIN PGP SIGNATURE-----
>
> iQEcBAEBCAAGBQJWTDBlAAoJEIZIHiXiz9k+ChIH/0E1rHDycXUB4ctrzvWWWq/z
> gR2Y2krA9+MiypWmfwgkcgeKhvxKICtLk4KOee3bqZOaRZRNlj9lhvzT1tfoVyo9
> diIr5S+EqZnCy0MjOzeUJVAw46em0L9AhvsQtys3Xl0euNOb+41hB9kecfLOfSHp
> wJnnxg39++oOKV7fkM8Dzb62p115VHiSEXjle5UzcbdIAuX/IkO9v4h6hJUZsWRj
> JOkBnAr0prUrhmpR3xe9uLK3WZ995nNreBOX6M2LGA8hDtOshniBRUsEQLJ2ucC9
> kpqtHDUnitm90x+3L7P52UcwoTN/P6WhI986pmNoDHiL3ZdMUAZ/KVxlPcJlLGs=
> =Meqf
> -----END PGP SIGNATURE-----
> _______________________________________________
> The System Safety Mailing List
> systemsafety at TechFak.Uni-Bielefeld.DE 
> <mailto:systemsafety at TechFak.Uni-Bielefeld.DE>
>
>
> _______________________________________________
> The System Safety Mailing List
> systemsafety at TechFak.Uni-Bielefeld.DE 
> <mailto:systemsafety at TechFak.Uni-Bielefeld.DE>
>
>
>
>
> -- 
>
> --
>
> *José Miguel Faria*
>
> *Educed *- Engineering made better
>
> t: +351 913000266
> w: www.educed-emb.com <http://www.educed-emb.com/>
> e: jmf at educed-emb.com <mailto:jmf at educed-emb.com>
>
>
>
> ------------------------------------------------------------------------
> If you are not the intended recipient, please notify our Help Desk at 
> Email Information.Solutions at nats.co.uk immediately. You should not 
> copy or use this email or attachment(s) for any purpose nor disclose 
> their contents to any other person.
>
> NATS computer systems may be monitored and communications carried on 
> them recorded, to secure the effective operation of the system.
>
> Please note that neither NATS nor the sender accepts any 
> responsibility for viruses or any losses caused as a result of viruses 
> and it is your responsibility to scan or otherwise check this email 
> and any attachments.
>
> NATS means NATS (En Route) plc (company number: 4129273), NATS 
> (Services) Ltd (company number 4129270), NATSNAV Ltd (company number: 
> 4164590) or NATS Ltd (company number 3155567) or NATS Holdings Ltd 
> (company number 4138218). All companies are registered in England and 
> their registered office is at 4000 Parkway, Whiteley, Fareham, 
> Hampshire, PO15 7FL.
> ------------------------------------------------------------------------
> _______________________________________________
> The System Safety Mailing List
> systemsafety at TechFak.Uni-Bielefeld.DE
> José Faria <mailto:jmf at educed-emb.com>
> 18 November 2015 at 10:18via Postbox 
> <https://www.postbox-inc.com/?utm_source=email&utm_medium=sumlink&utm_campaign=reach>
> >> "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'
>
>
>
>
> -- 
> --
> *José Miguel Faria*
> *Educed *- Engineering made better
> t: +351 913000266
> w: www.educed-emb.com <http://www.educed-emb.com/>
> e: jmf at educed-emb.com <mailto:jmf at educed-emb.com>
>
> _______________________________________________
> The System Safety Mailing List
> systemsafety at TechFak.Uni-Bielefeld.DE
> Klaus <mailto:klaus_sievers at web.de>
> 18 November 2015 at 10:13via Postbox 
> <https://www.postbox-inc.com/?utm_source=email&utm_medium=sumlink&utm_campaign=reach>
> 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
>
>
>
> _______________________________________________
> The System Safety Mailing List
> systemsafety at TechFak.Uni-Bielefeld.DE

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.techfak.uni-bielefeld.de/mailman/private/systemsafety/attachments/20151118/6b418740/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Banner-signature.png
Type: image/png
Size: 47783 bytes
Desc: not available
URL: <https://lists.techfak.uni-bielefeld.de/mailman/private/systemsafety/attachments/20151118/6b418740/attachment-0001.png>