Friday, March 27, 2009

Deice class

Taught a weather class to Brampton Flight Centre diploma students today.

Here's a cut and paste of an article I wrote for Weatherwsie magazine two years ago.

De-Iceman Cometh


At 4:01 p.m. on January 13, 1982, Air Florida
Flight 90 crashed into the ice-filled Potomac
River just 30 seconds after takeoff from
National Airport in Arlington, Virginia.
Seventy-eight individuals died in the
crash, including four people who were in
cars on the 14th Street Bridge spanning
the Potomac. Five passengers from the plane survived
the crash, due largely to the efforts of passersby and
emergency personnel who plucked people from the
frigid waters. The story of what happened on that
January day is one of tragic human error in the
face of extreme weather conditions; following the
crash, the National Transportation Safety Board
determined that the cause of the accident was icing
on the aircraft and the failure of the pilots to abort
the takeoff or use all of their anti-icing equipment.
In the years since the crash of Air Florida Flight
90, the industry’s approach to de-icing aircraft has
changed considerably. What once could have been
characterized as a "laissez-faire" system of plane
de-icing has morphed into a strictly regimented
program with new regulations that have eliminated
any room for doubt. No place better illustrates the
new era of plane de-icing than the Central Deicing
Facility (CDF) at Toronto’s Lester B. Pearson
International Airport. As one of the most northerly
countries in the world, Canada must take its plane
de-icing seriously, and the CDF’s massive complex
illustrates just how committed the country’s airline
icing industry is to safety.

Tragedies Prompt a Change in Regulations

Unfortunately, the first history of commercial air
travel is dotted with tragedies much like that of Air
Florida Flight 90. On Dec. 12, 1985, a large DC-8
aircraft loaded with American soldiers rolled off the
end of the airport runway in Gander, Newfoundland,
in freezing drizzle, killing 248 U.S. soldiers
and 8 crewmembers. For years the telltale scar it
gouged in the terrain acted as a vivid reminder of the
problems that ice on wings can cause. Meanwhile,
the crash of a commuter jet in Dryden, Ontario,
Canada, in 1989 further brought to light the perils
of airframe icing. The Fokker 28 aircraft crashed 15
seconds after takeoff, unable to achieve enough altitude
to clear the trees beyond the end of the runway
due to ice and snow on the wings. The crash resulted
in the deaths of 21 of the 65 passengers and 3 of the
4 crew members.

In the early years of commercial air travel, the
decision to de-ice a plane was made by the captain
or the airline. Throughout the industry, there was
a tendency to resist de-icing as much as possible
because of time constraints, low operating budgets,
and a general lack of knowledge about the perils of
ice on an aircraft. Use of technology was limited,
particularly for smaller cargo or charter companies
whose airplanes sometimes did not have amenities
such as heated windshields. In one case, a pilot was
equipped with a car windshield scraper to scrape the
ice off the plane’s windscreen from a side window
while on approach.

Meanwhile, although it was technically illegal for
an airplane to take off with ice-contaminated wings,
a gray area existed because the decision was generally
left to the captain’s discretion. For example, if a light
snow was falling, some pilots would elect not to deice,
thinking that the snow would blow off. In most
cases, it probably would, but as the history books can
attest, there are always exceptions. In the case of the
Air Florida flight that crashed into the Potomac,
the aircraft’s crew attempted to de-ice the aircraft
by intentionally positioning it near the exhaust of
the aircraft ahead in line, against the regulations in
their flight manual. This may have contributed to
the adherence of ice on the wing leading edges and
to the blocking of the engine’s probes.

In both the United States and Canada, it took a
horrific crash related to airframe icing to instigate
a change in de-icing regulations. In Canada, it was
the crash of the Fokker 28 commuter jet in 1989
that proved to be the impetus for changing deicing
regulations. In the United States, the crash
of USAir flight 405 from LaGuardia on March 22,
1992, instigated changes by the Federal Aviation
Administration (FAA). In the aftermath of the
crash, which resulted in 27 fatalities, the NTSB
found that although the plane had been de-iced
twice before leaving the gate, the time between the
second de-icing and take-off (35 minutes) exceeded
the "de-icing fluid safe holdover time" for that
particular type of fluid. The result was a buildup of
ice on the wings that resulted in aerodynamic stall
shortly after lift-off. According to the post-accident
report by issued by the NTSB, "the entire airline
industry had been lax in training crews to detect
hazards caused by ice and to compensate for such

These days, any second-guessing is removed from
the equation, and the old gray area no longer
exists. Both Canadian and American regulations
now prohibit take-off when ice, snow, and frost
is adhering to any critical surface of the aircraft,
including lifting and control surfaces, wings and
tail, and upper fuselage surfaces on aircraft with rearmounted
engines. The rule is known as the "clean
aircraft concept."

The main exception to the new regulations allows
a coating of frost up to one-eighth of an inch thick
on wing lower surfaces in areas cold-soaked by fuel,
between the forward and aft spars. De-icing also is
not mandatory if the captain expects dry snow lying
on top of a cold, dry, and otherwise clean wing to
blow off during take-off. For aircraft types where the
upper fuselage is a critical surface, a thin coating of
frost is permitted in the area provided the deposit is
thin enough that underlying surface features such
as paint lines, markings, or lettering can be distinguished.
Although pilots are in charge of deciding
whether de-icing is needed, the "lead" ramp atten-
dant can overrule a decision not to de-ice. Even
flight attendants and passengers can voice concerns
about the plane’s de-icing efforts, although the final
decision rests with the pilot.

Why a Clean Wing?

Many believe ice on the wings of an airplane is
dangerous solely because of the additional weight
on the aircraft. However, it is actually loss of lift
and the resulting drag on the body of the aircraft
that causes problems. Airplanes achieve lift when
air flows smoothly over the contoured surface of the
wing. If this streamlined flow is disrupted because of
ice buildup, decreased lift occurs. A wing can lose
30 percent of lift with just a small accumulation
of ice. The stall speed, or the speed at which the
wing ceases to be able to keep the aircraft aloft,
can decrease by 15 percent with drag potentially
increasing by 200 to 500 percent.

For example, a unique ice formation composed
of clear ice that builds up into a single or double
horn on critical surfaces can severely disrupt airflow
and increase drag 300 to 500 percent. Meanwhile,
ice, frost, and snow that accumulate to the thickness
of medium or coarse sandpaper on the leading
edge and upper surface of a wing can reduce wing
lift by as much as 30 percent and increase drag by
40 percent.

Toronto’s Central De-Icing Facility

In Canada and similar locales, icing conditions
can lurk nearly nine months of the year, so the deicing
checklist is always within reach because it’s
part of doing business. The old aviation adage, "If
you think safety is expensive, try having an accident,"
is a rule to live by.
The CDF at Toronto’s Airport is the largest deicing
facility in the world. Fully operational since
the 1999-2000 cold season, this 65-acre "drive
through airplane wash" consists of 6 huge bays
capable of handling hundreds of aircraft daily. It
has an official de-icing season of October 1-April
30. Many pilots jokingly refer to the CDF as the
"central delay facility," but the fact that most pilots
are paid by the minute takes the sting out of any
wait. In addition, the short time it takes to spray a
plane with de-icing fluid is insignificant compared
with the potential for disaster if a pilot did not take
the time to de-ice his or her aircraft.
Moreover, the CDF has actually reduced time
between de-icing and takeoff because it was built
closer to the runways and has increased overall
throughput and improved turnaround times.
On the way to the CDF, after passengers have
boarded the plane, pilots radio "pad control," which
assigns the aircraft to a de-icing bay. Because this
is a "live" or "engines running" operation, precise
terminology and electronic signboards are used to
eliminate any potential for accidents. Pilots then
contact the "Iceman" in the de-icing control center,
appropriately nicknamed the Icehouse.
Once the aircraft is in position to receive the deicing
spray, a machine called the Denmark Vestergaard
Elephant Beta springs into action. Smaller
planes might need only one Beta for de-icing, while
larger jumbo jets might need as many as four.
The CDF has 27 Beta machines, each of which
costs about one million Canadian dollars, or about
$876,000 U.S. The iceman tells the pilot the exact
time de-icing started, the type of fluid used, and
when the vehicles have retreated to their safety
zones. A safety zone is an area ensuring a safe distance
between the aircraft and de-icing vehicle.
The de-icing vehicles must be behind these lines
before an aircraft can exit the de-icing area.
While many airports still employ manually operated
"cherrry pickers" staffed by ground crew who
must brave the bitter winds and back spray, the CDF
machines are operated remotely by the Iceman from
a heated enclosed cab. They are armed with deicing
fluid, nozzles, whisker-like probes to prevent
aircraft contact, and a telescopic boom to reach
distant spots and critical flight surfaces.
The de-icing procedure involves spraying fluids
that remove or prevent ice build-up all over the
aircraft. Strictly speaking, de-icing refers to the
removal of existing ice, while anti-icing prevents
new ice from forming. Made up of combinations
of glycol and water, de-icing and anti-icing fluids
come in different varieties that each serve a specific
function. The difference between the types of fluid
is the "holdover time," or the time from when deicing
commences to the time the airplane must be
airborne, based on temperature, precipitation rate,
and type. For example, with Type I fluid at -3°C in
light snow, the holdover time is about 40 minutes.
For most operations, the de-icing Type I fluid is used
to remove the snow and ice, and Type IV is used to
prevent further adhering of ice.
As an airplane is being de-iced, all of the extraneous
fluid that falls off the aircraft is collected in
holding tanks to ensure compliance with environmental
regulations, as de-icing fluid can be a hazard
to nearby bodies of water. The tanks can hold up to
3,434,237 gallons of reclaimed fluid. Some of the
spent fluid is used to make car windshield wash and
engine coolant, but it cannot be re-used for airplane
de-icing because possible degradation of the fluid
means that its effectiveness cannot be guaranteed.
Air Canada prohibits the use of recycled fluid.
According to Joe Forbes, Senior Manager of Deicing
Operations at the Greater Toronto Airports
Authority, a typical Airbus A320 that holds about
150 passengers in light snow conditions requires 80
gallons of Type I fluid and 69 gallons of Type IV
fluid, with actual de-icing time taking just over 4
minutes. The throughput time at CDF for an Airbus
is an amazing 12 minutes.

At more than four dollars per gallon for Type
I and double that for Type IV fluid, de-icing an
airplane is an expensive proposition. During one
3-day ice storm in April 2003, the CDF used
396,258 gallons of de-icer in a single day, the highest
amount in the facility’s history. At one point
the CDF actually ran out of de-icing fluid and
scrambled to get more from Chicago, Denver, Forth
Worth, and Montreal, Forbes said. One truckload
of 4,497 gallons that was brought in from Chicago
was dispensed on a single jumbo aircraft. Because
de-icing fluid has a limited shelf life once it has
been sprayed on an aircraft, pilots consult onboard
charts and consider current temperatures and types
of precipitation to determine how long they have
before they must get airborne. If the take-off is
delayed for any reason, they may need to head back
for a re-spray.

In-Flight Ice Formation

Airframe ice does not occur only on the ground.
Although there exist some 30 variables when it
comes to the formation of ice on an aircraft in
flight, the two primary factors are visible moisture
(clouds) and freezing temperatures. Clouds contain
supercooled water droplets, which are composed of
water in a liquid state, even though temperatures
are below freezing. When a super-cooled droplet
strikes an aircraft, it freezes upon impact. To
prevent such freezing, airliners are outfitted with
heated leading edge wings that are warmed by the
hot air bled from engines. Heated windscreens,
instruments, and engine probes and intakes, as well
as continuous use of engine igniters, all aid in the
battle against ice accumulation.
In turboprop aircraft, electric heaters de-ice the
large rotating propellers. Turboprops also have a
rubber cover called a "boot" along the leading edge
of the wing. The boot can be expanded during the
flight to break off any ice that has attached itself to
the aircraft. In 1994, an American Eagle ATR-72
turboprop plane succumbed to airframe icing while
stuck in a holding pattern near Chicago. The plane
went down in an Indiana bean field, killing all 68
people aboard, after ice on its wings forced it to spin
violently out of control. The culprit was a design
flaw allowing ice to form aft of the boot.

In the United States alone there are an average of
50 aviation accidents each year involving airframe
icing. However, the number of such accidents has
decreased in recent years, in part because of the
stricter regulations and the construction of more
effective anti-icing facilities like the CDF. Most airframe
icing accidents now pertain to lower-tier general
aviation operations and private aircraft. In fact,
thunderstorms are responsible for more crashes and
deaths in the airline industry than icing; in 2004,
thunderstorms caused 14 crashes and 28 deaths,
compared with 12 crashes and 25 deaths for airframe
icing. As improvements continue to be made in
airlines’ de-icing systems and engineers continue to
find new ways to address airframe icing on aircraft,
perhaps one day the risk of aviation accidents caused
by ice will be eliminated altogether.

Just the facts about the CDF

Most aircraft de-iced/anti-iced in a day: 513
(February 3, 2000).
Most fluid dispensed in a season: Just over
7.5 million liters (1,981,290 U.S. gallons) in the
2002-2003 winter season.
Most aircraft de-iced/anti-iced in a year:
14,299 in the 2004-2005 season.
Most aircraft de-iced/anti-iced in one month:
4,200 in January 2004.