Planes crash due to the cumulative effect of small human errors, not single catastrophic failures. Studies show crashes typically result from 7 consecutive errors. Poor communication and mitigated speech among pilots, where concerns are subtly hinted at rather than directly stated, have contributed to crashes when pilots miss or ignore hints due to fatigue or cultural norms. Training aims to reduce mitigated speech and establish clear procedures for escalating safety concerns, even if it means relieving the captain temporarily, to prevent crashes from cascading errors.

1. Why do planes crash?
Michael Toppa
University of Pennsylvania
Perelman School of Medicine
Information Services
July 28, 2011

2. Why do planes crash?
 It'snot like the movies
 “The typical commercial jetliner is about as
dependable as a toaster”
 Poor weather
 Tired pilots, awake more than 12 hours
 Behind schedule, so the crew is hurrying
 Pilot and co-pilot have not flown together
before

3. The cumulative effect of small
errors
 Crashes
are the result, on average, of 7 consecutive
human errors
 No single error is disastrous, but the cumulative effect is
 Studies
show this is typical in disasters involving any
complex system
 The 3 Mile Island nuclear disaster was the result of 5 minor,
consecutive human errors
 I believe there are lessons here for our work as well
 Poor communication among the crew is a key factor

4. Mitigated speech
 Whenwe try to downplay or sugarcoat the
meaning of what we say, because we're
 Being polite
 Feeling embarrassed
 Being deferential to authority

5. Hypothetical scenario
 In a research study, pilots were presented
with a hypothetical scenario, and asked how
they would handle it
 They are in the role of co-pilot, they see bad
weather ahead, and they want to make sure
they don't fly into it.
 What do they say to the pilot?

6. 6 possible responses
1.Command: “turn 30 degrees to the right”
2.Crew obligation statement: “I think we need to
deviate right about now”
3.Crew suggestion: “Let's go around the weather”
4.Query: “Which direction would you like to deviate?”
5.Preference: “I think it would be wise to turn left or
right”
6.Hint: “That return at 25 miles looks mean”

7. The responses
 Pilots with the rank of Captain
overwhelmingly chose the “command” option
 Pilots with the rank of First Officer
overwhelmingly chose the “hint” option
 This may seem alarming, because it is!
 “A hint is the hardest kind of request to
decode and the easiest to refuse”

8. 1982 Air Florida Crash
 The plane had a problem with wing ice before takeoff
 First officer: “Look how the ice is just hanging on his,
ah, back, back there, see that?”
 First officer, again: “Boy, this is a, this is a losing battle
here on trying to de-ice those things, it gives you a
false sense of security, that's all it does.”
 The captain doesn't get the hint, and the plane plunges
into the Potomac river a few minutes after take off.

9. Avianca Flight 052
 The captain is exhausted
 Planes are normally very low on fuel when landing, but
this flight is literally running on empty
 First officer to ATC: “Climb and maintain three thousand
and, ah, we're running out of fuel, sir”
 ATC responds with a command to continue circling, and
asks for confirmation it's ok.
 First officer to ATC: “I guess so. Thank you very much”
A flight attendant enters the cockpit, and the engineer
makes a throat-cutting gesture to her
 Two engines flame out and the plane crashes

10. KAL Flight 801
 The captain is experienced, but exhausted,
it's night, and the weather is terrible
 The captain has flown to this airport several times
before
 He decides on a visual approach, using the
airport's beacon to navigate
 He's forgotten the beacon is on a mountain near
the airport

11. KAL Flight 801, continued
 First officer: “Don't you think it rains more? In
this area, here?”
 Engineer: “Captain, the weather radar has
helped a lot”
 They are trying to tell the captain they shouldn't
be making a visual approach
 Korean language and culture makes it more
difficult to speak directly
 The plane crashes into the mountain

12. Dealing with mitigated speech
 Crashes are more common with the Captain in the flying seat
 “Planes are safer when the least experienced pilot is flying,
because it means the second [more experienced] pilot isn't
going to be afraid to speak up”
 For 15 years the airline industry has trained flight crews on
reducing mitigated speech
 Standardized procedures for escalating communication
 If necessary, temporarily relieving the Captain of duty
 KAL switched to English-only in the cockpit

13. Example from The Clean Coder
 Mike: “Paula, I need the login page done by
tomorrow”
 Paula: “Oh, sorry Mike, but it's going to take
more time than that”
 Mike: “When do you think you can have it
done?”
 Paula: “How about two weeks from now?”
 Mike: (scribbles something in his daytimer)
“OK, thanks”

14. Passive Aggressiveness,
Saying No
 By not speaking more firmly, Paula is inviting
doubt about her estimate
 What if Mike went to his boss and blamed
Paula for the project being late?
 That's “morally reprehensible” passive
aggressiveness
 Saying no can be the first step in a
negotiation towards the best possible
outcome