[SystemSafety] Miss vs Ms

[Bruce Hunter]

Back in February 1996 there was a Tail-strike incident on Air Canada
combined passenger and freight flight 899. Luckily there were no injuries
as a result of the incident and only scraping and minor buckling to the
fuselage.  It does show the importance of getting weight and balance
correct.

The interesting thing was that this was indirectly a result of updated
software errors in an update to the off-board load balancing computer on a
PC (ALPAC). Great lesson that dangerous software failures may not just
occur on integrated systems but on separate ancillary equipment as well.
You really need to check whether safety functions are dependent on external
systems reliability as well (e.g.  safety-related information,
functionality dependent on subscription currency, authentical key
expiration etc.)

Full report is still available
https://bst.gc.ca/eng/rapports-reports/aviation/1996/a96o0030/a96o0030.html

Bruce Hunter

On Mon, 12 Apr 2021 at 13:31, Eric Burger <eric.burger at georgetown.edu>
wrote:

> Depends on the regulatory regime. In the USA, the FAA realizes that the
> smaller the aircraft the higher the probability of getting unlucky on the
> distribution. Same in the UK. With larger numbers and larger aircraft,
> getting the statistical child wrong has much less impact.
>
> Note this was an IT failure, per the AAIB Bulletin. A FAA Statistical
> Child (82#) is less than half the weight of a Statistical Adult Female
> (179#). The UK’s numbers are 35 Kg / 60 Kg. However, the aircraft in
> question counts as a large aircraft by the FAA definition (187 passengers
> is much more than the cutoff of 71). It is possible that all of the Misses
> were sitting together in the front on one side, but even then, we are
> talking an error of 1200 Kg on a flight loaded to 66495 Kg (the discrepancy
> is slightly less insignificant, but still insignificant, as the zero fuel
> weight was calculated as 56,716, not the expected 57,916. I realize that
> when one is on the edge of W&B, a 2% error can be really bad, but this
> flight was nowhere near that (in this case, 61,688 Kg). The impact? The
> takeoff V numbers were off by one knot (0.7%). I’d bet dollars to donuts
> that would go unnoticed - anyone want to calculate how many feet that adds
> to the takeoff roll on a 737 that is accelerating? Would the pilot notice
> the plane was microscopically taking longer to hit V1?
>
> Now, if this was an Embraer E170 (~65 passengers) that error would be bad.
> For an ATR 42 (~40 passengers), that error could be close to catastrophic.
>
> > On Apr 8, 2021, at 12:26 PM, Hugues Bonnin <hugues.bonnin at free.fr>
> wrote:
> >
> > Ok, it’s obvious that weight is critical, my remark is not on that. My
> remark is on the deduction of the weight from the categorisation
> adult/child only ; as a group of child can be heavier than a group of
> adult, it seems questionable to base critical element in this
> categorisation.
> >
> > Regards
> >
> > Hugues
> >
> >> Le 8 avr. 2021 à 16:55, Peter Bernard Ladkin <ladkin at causalis.com> a
> écrit :
> >>
> >> 
> >>
> >>> On 2021-04-08 15:41 , Gareth Lock wrote:
> >>> Hugues,
> >>> The issue I can see would be when you have a smaller aircraft and
> therefore the impact of mass would be greater.
> >>
> >>> *From: *systemsafety <
> systemsafety-bounces at lists.techfak.uni-bielefeld.de> on behalf of <
> hugues.bonnin at free.fr>
> >>> IMHO, I don't see how this difference could lead to serious problems,
> >>
> >> 2.2% of the ZFW. Sure that can lead to problems, such as calculating TO
> thrust and balanced field length.
> >>
> >> A weight mismatch can also lead to balance problems, depending on the
> seating algorithm used by the airline, but in a 187-passenger aircraft I
> would expect not.
> >>
> >> PBL
> >>
> >> Prof. Peter Bernard Ladkin, Bielefeld, Germany
> >> ClaireTheWhiteRabbit RIP
> >> Tel+msg +49 (0)521 880 7319  www.rvs-bi.de
> >>
> >>
> >>
> >>
> >>
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