Page 28 - ARUBA TODAY

A28 SCIENCE
Friday 23 June 2017

Science Says: Why some airplanes don’t fly in high heat

By SETH BORENSTEIN and
DAVID KOENIG
Associated Press
WASHINGTON (AP) —
When it comes to getting
airplanes off the ground
in broiling weather, it’s not
the heat or the humidity.
It’s the air density.
Hotter air gets thin, mak-
ing it harder to take off
and land safely, mostly for
smaller jets.
That’s what has kept some
planes grounded in Phoe-
nix this week where tem-
peratures have been push-
ing 120 degrees.
Airplanes take off and stay
aloft because of lift, the
force from the movement
of air underneath the
plane’s wings that push it
upward.
“As air warms up, it ex-
pands and there’s fewer
molecules to be under your
wing,” said Lou McNally ,
professor of applied me-
teorology at Embry-Riddle At Phoenix Sky Harbor International Airport American Airlines regional jets sit on the tarmac as American Airlines says seven re-
Aeronautical University. gional flights have been delayed and 43 have been canceled because of a heat wave as temperatures climb to near-record highs
With less lift, “you need Tuesday, June 20, 2017, in Phoenix.
more of everything. You Associated Press
need more thrust to take
off. You need more dis- thrust or power and have and early morning to get racing down the runway altitude, a key measure-
tance (on the runway) to larger wings. Smaller jets around the heat problem. and not get up in time and ment of flight conditions.
take off. You need more that generate less thrust, Gulf carriers also tend to have to abort. Airlines can take other steps
distance to land. like Bombardier’s CRJ re- operate longer flights using And if it tries to land when when the temperature
You need more speed to gional jets, which have a larger planes that aren’t as the air is too thin and hot, climbs too high. They can
land. It gets to a point for 118-degree limit at Phoe- limited by high heat. that’s not good either be- lighten the plane’s load by
some aircraft that it gets nix’s elevation, are more In Phoenix, temperatures cause it can run out of run- selling fewer seats — a tac-
just too much,” he said. likely to be stuck in the around 118 are infrequent way, McNally said. tic American Airlines is using
High heat also means a heat. enough that airlines con- Before they fly, pilots con- in the Phoenix heat wave
plane climbs at a lower At Dubai International Air- tinue to use regional jets for sult a sheet that tells them — or reducing cargo. They
rate, said pilot Patrick port and other Gulf air- shorter trips. about the temperature, can take off with less than
Smith, author of the book ports, which are used to hot If a plane does try to take elevation and even humid- a full tank of fuel and then
“Cockpit Confidential .” weather, many flights — off beyond its tempera- ity — factors that go into stop somewhere cooler to
To compensate, planes but not all — arrive at night ture threshold, it may keep something called density refuel.q
have to generate more