Taking time to calculate weight and balance on the ground can save you some nasty surprises in the air. Consider the misfortunes of some pilots who didn't.
May 7, 1997
|About the Author ...
Brian Jacobson has over 12,000 hours
in all types of general aviation aircraft from trainers to jets. He has been
flying since 1970, and earned most of his certificates and ratings on the East
Coast in the early 1970s.
His first aviation employment was as sales manager at Air Worcester, Inc.,
an FBO in Massachusetts. Through the years, he worked for several FBOs selling
airplanes and flying charters. For nine years, he was chief pilot for a division
of ITT based in Providence, Rhode Island, and later was a bizjet captain for
Textron, Inc., out of Providence, Augusta, Georgia., and Pontiac, Michigan.
During those years, he flew real-world IFR in all sorts of weather and some of
the most congested airspace in the world.
Since 1988, Jacobson has been a member of
the National Aircraft Appraisers Association, and owns and operates a firm
called Great Lakes Aircraft Appraisal, appraising airplanes for buyers, sellers
and financial institutions. He also helps individuals and businesses buy
aircraft by evaluating their needs, recommending the type of aircraft they
should purchase, and helping them locate and procure those aircraft.
Jacobson is also a professional aviation writer. He is a contributing
editor for AVweb, Aviation Safety, and IFR
Refresher; a contributor to Plane &
Pilot; and can be heard on Belvoir Publications' Pilot Audio
In October 1996, he published his first book,
Flying on the
Gages, in which he discusses his experiences flying IFR. In May, 1997, his
second book was published:
Purchasing & Evaluating Airplanes.
Are you looking for trouble?
You know as well as I do that looking for trouble isn't conducive
to a long and safe career in aviation. But, we all have probably
launched on trips without running the weight-and-balance numbers.
And, in doing so, we may have inadvertently punched a few holes
in the weight-and-balance envelopes established by the manufacturers
of our aircraft.
Weight-and-balance limitations are there for very good reasons,
most involving the safety of the occupants while the aircraft
is in flight. When we disregard them, knowingly or unknowingly,
we are looking for trouble.
Take, for instance, the hapless pilot of a Cessna 402 who attempted
to transport nine members of a varsity basketball team in his
airplane. The pilot did not get the accurate weights of the individuals
and their luggage. As he entered the cabin to close the door,
the airplane tilted over onto its tail...not an uncommon occurrence
for that type of airplane when too much weight is placed in the
rear of the cabin. The pilot and passengers got out of the airplane
and raised the tail. Then, the pilot decided to proceed with the
flight, still without having "run the numbers."
As he climbed through 300 feet AGL, he turned to those in the
cabin and yelled that he had a problem. He instructed his passengers
to move as far forward as they could. This apparently solved the
pilot's immediate "problem," but the airplane eventually
was landed with most of its passengers not seated with restraints
An inspection revealed that the 402's rear bulkhead, a stringer,
the elevator control tube and the housing for the tail navigation
light were damaged when the aircraft fell onto its tail. Investigators
ran the numbers using actual weights of the passengers and baggage,
and found that the center of gravity was well beyond the aft limit.
The pilot was very fortunate that he did not lose an engine during
the flight; the aft c.g. would have seriously aggravated the asymmetric
This may be an extreme case of weight and balance mismanagement
and total neglect of incurred damage, but the fact remains that
many of us don't pay enough attention to how we load our aircraft.
While we don't get into accidents every time that happens, there
can be consequences that we don't anticipate.
Ask, Don't Guess
There are compromises in the designs of almost every airplane
built. We can fill the cabin or the fuel tanks; but, normally,
we can't do both. Most of the time, we must juggle fuel and payload
to assure ourselves that the airplane is within the weight and
balance envelope. In some airplanes, like the Piper Seneca, the
c.g. may be forward of its limit with full fuel and only two people
aboard (in the front seats). In others, like the Beech Bonanza,
the numbers should be run both for takeoff and landing, since
the c.g. moves aft in a rather tight envelope as fuel is burned.
If you guess passenger and baggage weights, as the Cessna 402
pilot apparently did, you could find yourself playing test pilot
and operating outside the envelope. It's best to ask each individual
for their actual weight, check each piece of baggage as it is
loaded and run the numbers before takeoff.
Unfortunately, you don't see too many pilots standing around their
airplanes with calculators in hand. That's a shame, since it really
does not take a lot of time to run the numbers. There are special
plotters, calculators and computer programs for many aircraft
that produce results within a minute. I have a program that takes
the weights of passengers, baggage and fuel, and then shows me
where I stand in a graph, similar to that in the AFM.
Still, too many pilots load passengers and baggage with nary a
thought about weight and balance. The FARs don't specifically
require a record of weight and balance for noncommercial flights,
but all pilots are required to operate our aircraft within the
limitations prescribed by the manufacturer. We cannot be sure
we are doing so unless we run the numbers.
One quick-and-dirty method used by many pilots is what I call
the "half-of-the-equation" system: The pilot quickly
adds up the weights of the empty aircraft, passengers, baggage
and fuel, and gets a warm and fuzzy feeling if the sum is less
than the maxmum allowable takeoff weight. The balance portion
of the calculation is neglected altogether. This practice reflects
an ignorance of what "weight and balance" really is,
and of what flying an airplane out of its c.g. envelope could
mean to safe operation.
The balance side of the equation could be simply envisioned as
the airplane resting on a pinnacle, supported at its center of
gravity by one sharp point. As you add or subtract weight to the
aircraft, that balance point (e.g., the center of gravity) moves.
Add or subtract too much weight forward or aft, and the aircraft
will fall off the pinnacle. Before that happens, though, the pilot
will experience some handling problems. And, in some cases, those
problems can be serious enough to cause a loss of control.
For example, as the c.g. shifts closer to the horizontal tail
(toward the aft limit), the elevator becomes more effective the
stick forces required to make a pitch change become very light,
and the airplane becomes longitudinally unstable.
Production airplanes are designed to be longitudinally stable
when operated within their c.g. envelopes. You can "feel"
this when you push or pull the control wheel to make a pitch change:
The airplane, when trimmed for level flight, will try to return
to its trimmed condition. But, as the distance between the c.g.
and the horizontal tail decreases, the stick force required to
make a pitch change also decreases.
At the point of "neutral longitudinal stability," the
airplane will tend to maintain its present attitude instead of
trying to return to its trimmed condition. The stick force required
to make a change will be extremely light, and that could result
in overcontrolling. It's possible, in an extreme case, to get
into a pitch attitude so high that there won't be enough "down"
elevator travel to prevent, or recover from, the impending stall.
You've probably flown your airplane at one time or another with
the c.g. at or near the aft limit. You'll probably remember that
as you rolled down the runway, the airplane came off the ground
before you expected it to. You quickly trimmed the nose down,
realizing that although you set the trim forward of where you
normally would, it was not enough. Then, as you flew the airplane
away from the airport, you noticed that the amount of elevator
travel to effect a pitch change was much less than normal.
Some time ago, a Beech 18 captain lifted off from an Alaskan airport,
retracted the landing gear and found the aircraft trying to roll
to the left. He corrected with right aileron and attempted to
decrease the pitch attitude, but the aircraft rolled right and
then back to the left. He landed near the departure end of the
runway with the gear up.
Investigators discovered that no one had checked the weight of
the freight and that the airplane was 1350 pounds over its maximum
certified takeoff weight. Also, the c.g. was about three inches
aft of the aft limit. Did the pilot run out of forward elevator
because of the severe aft loading? We don't know that for sure,
but the rolling action of the airplane indicates it was in or
near a stall condition from the time the landing gear was retracted.
What may have happened is that the stick forces on the elevator
were so light because of the rear loading that, initially, the
pilot thought he had the airplane trimmed properly when it was
perilously close to a stall. When he realized that, in reality,
the nose was pitched way too high and tried to avoid the stall,
it was too late to do anything except allow the aircraft to settle
back to the ground.
The "behavior" of different airplanes loaded to an aft
c.g. varies. But, remember that the manufacturer designed and
certified your airplane to be operated within the c.g. limits;
and, once you get behind the aft limit, you are on your own. You
become a test pilot, and you relegate your passengers to playing
the role of potential crash dummies.
Exceeding the forward limit can be trouble, as well. As from the
time the c.g. moves forward, the controls become heavier. More
effort, and travel, is required to make a pitch change. The level-flight
trim position of the elevator is higher than nonmal; and, in some
extremes of forward loading, you could run out of elevator before
you accomplish the pitch change you want.
For example, you are beginning to flare for a landing and discover
that, even with full travel of the elevator, the pitch attitude
is not high enough to keep the nose wheel from striking the ground
before the mains do. In fact, at the point where you pulled the
throttle to idle for the landing, the nose would fall, the airspeed
would increase, and you couldn't do anything about it except
attempt a power-on landing probably at a higher airspeed than
Adding power would pitch the nose back up, but you'd need a longer
runway to help dissipate the extra speed.
On the Spot
Sometimes, it's hard to do an accurate "weight and balance"
because someone shows up with more luggage than you expect,
or it's obvious that some of your passengers didn't give you their
correct weights. But, you should always try to be certain that
the aircraft is within its weight and c.g. limits. Programmable
calculators can make a weight-and-balance problem easy to do
on the ramp with your passengers standing by the airplane.
Sure, doing it on paper would take a while; but if you know you
have a large load to go into your airplane and you don't know
the exact figures before hand, it would be much safer to delay
the flight and do the calculations than to cross your fingers
while stuffing the seats and baggage areas with as much as they
can physically handle. After becoming airborne and realizing that
the airplane is not behaving very well is the wrong time to
wonder about all the luggage you loaded in a rear baggage compartment.
In one case, a Piper Lance crashed during a night takeoff from
Great Barrington Airport in Massachusetts. There were five passengers
and the pilot aboard. They had flown in to go skiing but found
that the ski resort was closed. They decided to fly over to nearby
Pittsfield, where they knew they could ski. On takeoff, the aircraft
hit the top of a 60-foot tree nearly 500 feet from the departure
end of the runway.
Two of the occupants died. Investigators determined that the
aircraft was 368 pounds over its maximum certificated weight and
loaded outside the aft c.g. limit. The runway was just under 2600
feet long, and it was the first time the pilot had flown into
The NTSB report I reviewed did not say where the flight originated
or whether the pilot bought any fuel at Great Barrington; but,
if he did not, then the aircraft loading was farther out of tolerance
on the leg before the crash occurred. It seems as though this
pilot loaded the airplane according to the number of seats and
amount of baggage space it contained, rather than considering
the full impact of weight and balance.
If you always fly your airplane with the same load, it is probably
not necessary to do a weight and balance each time; you should
know where you stand in the c.g. envelope. But, when something
changessomeone unexpected shows up, or more luggage than you
anticipated is sitting on the ramptake the time to do a thorough
weight and balance calculation.
Remember, the manufacturer's limitations are the result of tests
of handling characteristics within the envelope (there is little
or no testing outside the envelope). By flying outside the envelope,
you are not only testing your aircraft and your piloting skills,
but, also, the ever-present law of Mr. Murphy.