[Music]
many of you have probably experienced
those
few minutes of sitting in an airplane on
the runway waiting for takeoff
annoyed and wondering what is taking
them so long
it's our turn the runway is clear and
we're still not moving
for comparison a nimitz-class carrier
can launch one aircraft every 20 to 30
seconds from its four catapults
so why can't our airports do better
those two to three minutes of wait in
between takeoffs
is to guarantee your safety
as an airplane passes through the air a
disturbance forms behind it
known as wake turbulence wake turbulence
has two major components
jet wash and wingtip vortices jet wash
is the rapidly moving gas that's
expelled by the jet engines
it's extremely powerful and hazardous
jet wash can easily flip
cars the good thing is that the effect
of jet wash is relatively
short-lived on average jet wash is
experienced up to 400 feet with the
exception of takeoff thrusts which can
extend to 1900 feet behind the aircraft
but on the other hand wingtip vortices
are the primary and the most dangerous
component of wake turbulence they are
disturbances that occur
as a result of the wing generating lift
and can remain in the air for up to
three minutes
and stretch up to 10 miles aircraft
wings
generate a pair of vertices that rotate
in opposite directions
and sink about 290 to 490 feet per
minute
they are not true turbulence but still
are incredibly dangerous
because if one aircraft enters the wake
of a larger aircraft
it can lose its roll control due to the
rotating vortex
resulting in a flip over and crash
the strength of the wing tip vortices
depends on the speed
wing shape and the weight of the
aircraft altitude also
plays a factor as the strongest vortices
form below
2000 feet so you can see how wake
turbulence presents a huge hazard for
aircraft during takeoff and landing
over the years wake turbulence caused
numerous accidents
taking away hulls and lives but it took
this next incident
for the officials to finally take some
action
on may 30 1972 a dc-9
aircraft was performing touch-and-go
landings behind a larger
dc-10 aircraft when it encountered wake
turbulence
rolled 90 degrees and crashed into the
runway
during the follow-up investigations the
national transportation safety board
conducted a series of
wake vortex tests using lockheed l-1011
and dc-10 aircraft a colored smoke was
emitted from a tower
and observations of the smoke after the
aircraft flew by the tower
gave the team insights about the length
of time that vortices would remain in
the air
after the aircraft had flown by it's
worth noting that not only you can see
wingtip vortices
but sometimes you can also hear them as
rustling and cracking sounds
as a result of these experiments the faa
developed minimum separation standards
that take into account the effect of
wingtip vortices from a departed
aircraft onto the one that's departing
after
under these rules airplanes were to be
classified into light
medium and heavy depending on the weight
of the aircraft
later on a superclass was also added to
the categories on an interim basis for
the airbus a380
and antonov an225 while classified as a
medium
the boeing b757 has special wake
turbulence separation criteria
after numerous incidents of smaller
aircraft losing control when following a
b757
during takeoffs an aircraft of a lower
weight category
has to wait at least two minutes before
flying after an aircraft of a higher
weight category
if the following aircraft does not start
its takeoff role from the same location
as the preceding aircraft
the weight interval is increased to
three minutes to ensure the wake
turbulence has dissipated
during landings the weight category of
the preceding airplane and the following
airplane
determine the minimum separation
distance for example
if a light aircraft is landing after a
super the minimum distance between the
two aircraft should be eight nautical
miles
but if a light aircraft wants to land
after a medium aircraft
the minimum separation distance is just
four nautical miles
both minimum time and minimum distance
separations
can severely limit the throughput of an
airport and result in delays and traffic
jams
what we just discussed were the rules in
the united states
but not all countries follow the exact
same rules
for instance in dubai an airbus a380
is not part of a special category like
it is in the u.s
because it would severely impact the
dubai airport's efficiency
so the double decker is just treated
like any other heavy aircraft in most
situations
safety is second i suppose air traffic
controllers are legally responsible for
making sure there's sufficient time and
distance separation
between aircraft before giving them
clearance to take off or land
but on busy days they often have to lead
clearances
or cheat in other words they assume that
preceding aircraft would be added away
and have sufficient separation before
giving clearance to the following
aircraft
but by doing that air traffic
controllers do not really break
regulations
they account for things like spooling up
the engines before the aircraft actually
moves this technique only saves a few
seconds
but over the course of a day it adds up
significantly
[Music]
in order to increase airport efficiency
in 2012
faa began a pilot project of testing
revised criteria which relied on a six
category system
instead of the previous four category
system
this new system takes into account not
only the weight of an aircraft but also
the approach
speed and wing configuration the pilot
project was implemented in memphis
tennessee
and resulted in 15 increased capacity of
the airport's daily takeoff and landings
due to reduced minimum separations under
the new system
this new system is currently implemented
in more than a dozen airports across the
united states
if what we discussed so far made you
more scared of flying
then you may want to skip this next part
can wake turbulence flip airplanes
mid-flight
in march of 2017 while a challenger 604
was mid-flight
an airbus a380 was traveling a thousand
feet
above the challenger but in the opposite
direction
48 seconds after the two crossed paths
at a distance of 15 nautical miles from
the airbus a380
the challenger encountered severe wake
turbulence that rolled the aircraft
three to five times and flamed out both
of its engines
the challenger 604 lost ten thousand
feet in altitude before the crew was
able to bring the aircraft under control
due to the extreme g-forces experienced
the aircraft
was damaged beyond repair and was
written off
as a result of this incident there is
now a worldwide concern
regarding the wake effects of the airbus
a380
it's always the little guy that gets
hurt
finally let's go back to the aircraft
carriers for a moment
while the width of a flight deck is
roughly equivalent to the width of an
airport runway
the airplanes that are launched from a
carrier are much smaller
in addition the carrier launch airplanes
are also
usually of similar size which means the
wake turbulence
is less impactful also keep in mind that
the carrier is traveling
into the wind which in turn reduces the
wake turbulence
and last but not least the jet aircraft
that take off from the carrier
perform a clearing turn to the right of
the bow and to the left of the waste
catapults
this allows for nearly simultaneous
launching of two aircraft
however if the aircraft climbs straight
ahead a minimum interval of 30 seconds
between aircraft launches is needed
the moral of this story is the bigger
you are
the harder they fall
[Applause]
[Music]