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# Boeing admits flaw in 737 Max flight simulator

Rumours & News Reporting Points that may affect our jobs or lives as professional pilots. Also, items that may be of interest to professional pilots.

# Boeing admits flaw in 737 Max flight simulator

24th May 2019, 13:00

Join Date: Mar 2019
Location: Spokane, WA
Posts: 12
I wonder if the statement about designing for the average crew pertains only to the pre-certified phases of aircraft design, with the assumption that certification thresholds will then be created from whatever competence must be demonstrated to safely handle the certified aircraft? (Which if the idea of "designed for the average crew" is followed carefully, will not require any exceptional pilot skill to pass, just just careful, complete training.)

I can't see any other reasonable way to parse language like that.
24th May 2019, 17:59

Join Date: May 2019
Location: USA
Posts: 1
Originally Posted by compiforce
Not all natural distributions are Normal. However, very many are, because of the Central Limit Theorem. In essence, if a physical measurement is the sum of smaller figures, it is very likely to be Normal. That's why heights of people are approximately Normal, IQs are roughly Normal, etc.
It would be very surprising if the performance of pilots differed much from a Normal distribution.
A Normal (or Gaussian) Distribution is entirely described by its mean and variance. So, unless the distribution of performance of pilots is very unusual (such as a Laplace Distribution), the only relevant features of the distribution of pilot performance will be the mean (or average) and the variance (which determines how many are in the "tails" and how long the "tails" are).
Central limit theorem does not constrain population distributions or individuals. It tells us that sample means will be normally distributed independent of the distribution of the population. That arises because there is a Gaussian process built-in: random sampling. That is damn clever! This has nothing to do with having confidence about how any population is distributed, and in fact is useful specifically because most populations are not normal.

Take human height. It's bimodal, and pretty heavy on the low-end. It's more "approximately" normal if you stratify by gender and age. Even then... ~5% of the people will be wildly outside of the expected distribution. For them, designs that rely on the normal distribution to define the likely minimum and maximum would be laughably inappropriate. And if you only considered mean and standard deviation as relevant and disregarded gender and age... decisions could be way off for groups that aren't randomly assembled (e.g., Ms. Johnson's 1st grade class). Now, I'm emphasizing where the model is wrong even though it's right 95% of the time... but sometimes that 5% is important. As George Box wrote, it's not enough to disclaim that your model is approximate (aka sometimes wrong), you also have to be careful that it's not importantly wrong.

Does the complexity of flight training and review system result in the normal distribution holding in the in the area of the distribution where pilot skill interacts with automation failures to prevent recovery? That is a very interesting and compelling question! The answer has very useful implications. It's not a foregone conclusion of probability theory.

- a humble pilot.
25th May 2019, 03:42

Join Date: Jul 2007
Location: Auckland, NZ
Age: 75
Posts: 431
Originally Posted by hans brinker
Q: If the average applicant scores 100 points on the pilot qualification test, made up of theoretical questions, and a simulator check, you say they should probably normally distributed. Lets say 60 % score between 90 and a 110 points, and the airlines only hire the pilots with over 90 points. With the 20% percent who didn't cut it missing, wouldn't the resulting curve be non-normally distributed? (and seeing hiring rates around 50% at interviews makes me think the skewing would be worse)
Quite so. And while there will be an average level of skill for qualified pilots, the distribution is not at all likely to be normal, because you've selected the group, and the value will be pulled to the left by the sky gods.

Anyway, average is probably the wrong measure of central tendency. Better is almost certainly the median: by definition, half the population will be at or below the median value. Clearly, aircraft have to be readily manageable by the half of qualified pilots who fall below the median--especially aircraft like narrow-body twins, which are likely to fly the bread-and-butter routes that don't attract the profoundly gifted.

The issue, surely, is not to do with statistics, but with what the cut-off level is for getting, and maintaining, qualification (and it would be good if there were some measure of variability--you don't really want to have in charge of an airliner someone whose flying is sublime some days, but a total mare on others.)

25th May 2019, 08:07

Join Date: Feb 2015
Location: The woods
Posts: 1
Average etc.

In past years in my airline pilots were qualified after each check as
Above (later changed to High) average, Average, Below average (possibly requires extra training) and Failed (out if happens twice).
The average was supposed to be the average for that particular airline, which was supposed to be pretty good.
However this changed to Qualified and Not qualified (which required remedial action). I think that is what we have to look at - not whether someone has a licence - we all have a licence - but whether one is qualified to the professional standard demanded by the airline and stipulated by the manufacturer.
I for one would not like to be a pax in an airliner piloted by two guys who had a licence but had not passed stringent company requirements.
And by the way this qualification was applied on check rides and sim checks but there were also training (refresher) flights where all hell could be let loose to train combination failures. These were not qualified sessions but if someone screwed up further action (training) was given.

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