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"Overloading an aircraft can cut margin of safety"



Monday, August 27, 2001

Overloading an aircraft can cut margin of safety
By Ken Kaye
The South Florida Sun-Sentinel


Theoretically, an engine failure on takeoff in a small commuter aircraft
such as a Cessna 402B shouldn't result in a fatal accident. The plane is
designed to climb with only one of its two engines throbbing.

But stuff nine people on board, along with fuel, luggage and assorted
equipment, and the twin-engine plane might be at or above its maximum
allowable weight, reducing safety margins to almost nil.

Then even the most skilled pilot may not be able to overcome the aerodynamic
demons that can take hold of an aircraft when it is flying too slow and too
low and suddenly experiences power loss.

A twin-engine plane that falls below what's known as the minimum control
airspeed is prone to roll over and dive. Very abruptly.

I'm not necessarily saying excessive weight caused Saturday night's
accident, in which a Cessna 402B crashed shortly after takeoff from Marsh
Harbour in the Bahamas, killing nine, including R&B singer and actress
Aaliyah.

But the plane's weight and balance likely will be a factor as accident
investigators sift through the wreckage.

Primarily, they will focus on why the plane lost power shortly after
takeoff, and, for all we know, might find sabotage or fuel contamination at
the core of the calamity.

In any case, the accident shows why jets and turboprops have much better
safety records than small commuter planes when it comes to flying
passengers.

Even the smallest twin-engine jets are so powerful that they can still fly
overweight and climb with one engine out.

That isn't necessarily the case with the Cessna 402B, a plane commonly used
for charter and air taxi operations, particularly between Florida and the
Bahamas.

The aircraft has two 300-horsepower engines. Its maximum allowable weight is
6,300 pounds, of which up to 612 pounds is reserved for fuel and 1,650
pounds is permitted for passengers and luggage.

That means in the event one engine quits, one 300-horsepower engine is left
to keep more than three tons in the air.

The reality is that the plane can barely climb with that power-to-weight
ratio, and that is only if the pilot manages to build up sufficient airspeed
before the power loss.

In a normal twin-engine takeoff, the pilot will accelerate as rapidly as
possible to the minimum control airspeed. Whether the pilot in Saturday's
accident did so might never be known.

If he failed to achieve that speed, or if the plane was overweight and
required an even higher speed, his best hope of survival would have been to
poke the nose down immediately -- even at a low altitude -- to maintain
airspeed.

That, in turn, would leave some lift in the wings and thus some semblance of
control. Then, he would have had to put down straight ahead and hope there
weren't too many obstacles in the way.

And the reality there is this: Human instinct tells a pilot to keep pulling
up to avoid the ground, and that all to frequently results in a stall, or an
abrupt loss of lift.

Takeoff and landing accidents are among aviation's most prolific killers.

It should be noted that there is nothing inherently dangerous about flying
to the Bahamas. And many of the air taxi operators that go there are
perfectly legal and safe.

On the other hand, here is a fact: Air taxis, or operations that carry fewer
than 10 passengers per flight, do not have to fly under the same strict
safety standards of the scheduled airlines.

Their pilots do not have to undergo the same training and testing regimen
and the planes do not have to carry the same amount of safety equipment.
That's not to mention air taxi planes do not receive the high-degree of
maintenance.

As a result, the fatal accident rate for air taxis was .91 accidents per
100,000 flight hours last year.

In hard numbers, that translates to 22 fatal accidents that killed 71
people.

By comparison, for the same period, the scheduled airlines' fatal accident
rate was .017 accidents per 100,000 hours.

That included three accidents that killed 92 people (with the great number
of deaths due to the fact that airliners carry many more people per flight
than do air taxis).

So it is a bit puzzling to me that a troupe of people surrounding Aaliyah
settled on a small outfit with some question marks to fly them out of Marsh
Harbour.

That is an airport with a 5,000-foot runway, long enough to accommodate
corporate jets, and one that is serviced by American Eagle, a reputable air
carrier.

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