Gross Weight

How much is too much over gross weight?

This issue comes up so many times, sometimes I feel like writing an
overgross FAQ. The short answer is - it depends. Now for the long
answer:

Legal aspects:

Even 1 pound over max gross is not legal, and can subject you to civil
penalty - unless you have been granted some deviation. The deviaitons
come in many flavors. Many light aircraft in Alaska are eligible for
up to 15% increases if operated under Part 135 (obviously they fly
differently under Part 91). Some STC's allow you gross weight
increases with certain (often minor) modifications. Some engine change
STC's come in flavors where one gives you a gross weight increase and
the other does not - with the same engine. The FAA will give you a
ferry permit to operate up to 20% overgross without batting an eye if
you show that you understand what you're getting into.

In other words - understand that gross weights are as arbitrary as
speed limits - sometimes they exist for very good reasons, and may give
you very little margin for error (or even none at all, or less than
none), and other times they are arbitrary. It all depends on the
situation. But rest assured the FAA won't see it that way.

So how will you get caught? Well, you could have an accident. You
could be ramp checked - but in that case the overload would have to be
obvious and egregious - nobody will catch you on a 50lb overload. Put
four big guys into a Cherokee 140, though, and you are advertising an
overgross operation.

Insurance aspects:

Your insurance PRIMARILY covers you for pilot error, since that's
(officially, at least) the cause of most accidents. I've had many
insurance policies, and none have ever excluded coverage when operating
contrary to FAR's.

In other words, the idea that you're uninsured when overgross is a
myth. You're covered if you are drunk, overgross, and fly into an
airport without a clearance. Exemptions are clearly stated. Generally
they require you to have a certificate of a certain grade, certain
hours of experience, and an annual and medical that have not expired.

On the other hand, if you overload and fail to get off the ground, you
may have a hard time getting insurance after about the second or third
time this happens, and you will pay more the first time.

The slippery slope:

If you fly overgross, you're breaking the rules. Where will the
rulebreaking stop? The answer is really nowhere. It's like speeding -
you are substituting your judgment for regulation. Once you've shown a
willingness to do that, you will keep doing it when you feel it's safe
to do so. That's worth thinking about, assuming you never ever break
any regulations whatsoever, not only in your airplane but also in your
car, on your bicycle, etc. Otherwise, that ship has already sailed and
it's not a valid question.

A more on-point slippery slope - if 25 pounds over is OK, what about
50? And next time 100? 200? Where does it stop? That's the valid
question - and it has a valid answer, but not one you're going to like.

Simple light airplanes have a single maximum gross weight - one size
fits all (really one size fits nobody, because it's a compromise). The
bigger and more complex the airplane gets, the less true that is.

Some airplanes have zero fuel weights, because the wing attach points
are a weak point in the design. Some have a maximum takeoff weight
higher than the maximum landing weight, because the landing gear is a
weak point in the design. Some are eligible for gross weight increases
with tip tanks, provided the extra weight is fuel in the tip tanks and
nothing else. And when you get all the way up to the airlines, their
maximum takeoff weight depends on the runway length, the required climb
gradient, and the density altitude - in other words, it's not a single
number, but must be computed for every takeoff.

So how much is too much? It all depends on what sets the limit. On
some Cessnas, the limiting factor is being able to show the required
positive rate of climb with full flaps (40 degrees). Limit flap travel
to 30 degrees, and you get a 100 lb gross weight increase. Suppose you
simply limit travel operationally (and don't install the hardware)? Is
that OK? How about if the selector switch gets stuck in the down
position?

Are you protected if you stay within the rules? You only think so.
The gross weight is the same at 7000 ft density altitude as it is at
sea level - but at that density altitude, the plane will NOT climb with
full flaps at gross. Never forget, these limitations are arbitrary -
staying within them won't necessarily keep you safe, and breaking them
isn't necessarily dangerous.

It is possible (but not legal) for you to do the same thing the
airlines do - come up with your own calculations and procedures.
Sufficient data exist in the average POH to extrapolate performance
curves for various operations above gross weight, so you can estimate
takeoff, landing, and climb performance, compute new operational
speeds, etc. You can study the design, and the available modifications
and authorizations, to determine if it is performance, rather than
structural integrity of some component, that limits gross weight. You
can consider the nature of the flight - perhaps 3.0 positive gee limit
is sufficient on a smooth VFR day. In other words - you can approach
operation outside the established envelope the way a real, modern test
pilot does it.

Can the average private pilot do this? Will he? No, and no - and
that's why the rules are what they are. They are written to the lowest
common denominator.

Can you learn how to do it? Probably. If you have sufficient
technical background, you may do it on your own. Or someone can teach
you - but who? Not this guy:

I know that when I was receiving training, my instructor
once had me bring 2 male adults with me to a lesson.

He then had you project performance and handling characteristics by
extrapolating from the POH and maybe other sources. In flight, he
discussed these issues with you so you would know how to handle the
situation in the future, pointing out quirks of the operation. No? He
just told you to get in and go?

I wish that were the exception, but it's the rule. He was teaching you
how to fly overgross, and he was doing about the worst possible job of
it. Yeah - you did it in that particular instance. You learned a
little - mainly, you learned that operating outside the published
envelope has consequences, and a bit about what they can be. But
without an underlying framework for understanding, all you learned is
what happens in that one specific case. Since that specific case is
unlikely to be repeated exactly, you haven't really learned anything
very useful.

So the answer to your question of how much is too much? When the
safety margin associated with the limiting factor in play under the
circumstances becomes uncomfortably slim, that's too much.

Michael

"Michael" writes:

[...] In other words, the idea that you're uninsured when overgross
is a myth. You're covered if you are drunk, overgross, and fly into
an airport without a clearance. Exemptions are clearly stated.
[...]

As a contrary data point, my (Canadian Marsh/Lloyds) insurance
includes an explicit requirement to stay within W&B limits to retain
coverage.

- FChE

As a contrary data point, my (Canadian Marsh/Lloyds)
insurance includes an explicit requirement to stay within
W&B limits to retain coverage.

Which may or may not be enforcable, depending on state laws. It is
true, thought, that some carrier demand in-envelope operation, and that
others required the airworthiness cert to be in full force and effect,
and then argue that over-weight operation voids said cert. Again,
whether this latter approach would work would depend on the state.
Avemco, though, specifically say that you can be over-weight and
they'll still pay. And no-one has yet produce an example of *any*
company failing to pay as a result of an aircraft being over-weight....

Has anyone identified an accident that was caused by being overweight.
Are they common? Certainly not as common as running out of fuel.

On 8 Jul 2005 17:55:19 -0700, "Doug" wrote:

Has anyone identified an accident that was caused by being overweight.
Are they common? Certainly not as common as running out of fuel.

Plenty of accidents caused by being outside of the CG envelope.

I recall a Bonanza that crashed on takeoff leaving KASH with a load of NH
tax-free liquor.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Has anyone identified an accident that was caused
by being overweight. Are they common?

I've read of quite a few where over-weight operation combined with high
DA to result in an aircraft either running off the end of the runway on
take-off, or, worse, getting into the air and then spinning in upon
being unable to maintain a climb. I am quite convinced that over-weight
operation will cause accidents; I'm not convinced it results in
accidents as a result of structural failure.

"Michael" wrote in message
oups.com...
I know that when I was receiving training, my instructor
once had me bring 2 male adults with me to a lesson.

He then had you project performance and handling characteristics by
extrapolating from the POH and maybe other sources. In flight, he
discussed these issues with you so you would know how to handle the
situation in the future, pointing out quirks of the operation. No? He
just told you to get in and go?

I wish that were the exception, but it's the rule. He was teaching you
how to fly overgross, and he was doing about the worst possible job of
it. Yeah - you did it in that particular instance. You learned a
little - mainly, you learned that operating outside the published
envelope has consequences, and a bit about what they can be. But
without an underlying framework for understanding, all you learned is
what happens in that one specific case. Since that specific case is
unlikely to be repeated exactly, you haven't really learned anything
very useful.

So the answer to your question of how much is too much? When the
safety margin associated with the limiting factor in play under the
circumstances becomes uncomfortably slim, that's too much.

Michael


Very nice post, and I enjoyed reading it. I especially like your view on
what my instructor did, and you make a very good point. I have admitted to
myself, that he did some things in my training that, although we got away
with, were wrong, and I remember those each time I fly. You make a very
good point with regard to teaching without the proper framework. I will
also remember that. Thank you for you comments.

Fred

Excellent post!

I have two comments...

If you fly overgross, you're breaking the rules. Where
will the rulebreaking stop? The answer is really nowhere.

I agree. But as you pointed out earlier, keeping within max gross won't
keep you safe, either. In other words, every flight includes making
decisions about performance that are arbitary, or more precisely, that
are based on experience. If experience didn't matter, why would we keep
log books? If the rules were enough, why would we need anything else?

You can study the design, and the available
modifications and authorizations, to determine
if it is performance, rather than structural integrity
of some component, that limits gross weight.

If it is structural issues -- which I would suggest it very rarely is
-- you'll still have a huge safety margin when 5% or 10% over-weight.
You are not going to be getting that close to the 'g' envelope, and
your landings are hopefully not going to be hard enough to be given 10%
of collapsing the gear!

Further, if you look at accident reports where over-weight operation
was a factor, I doubt you'll find many where structural issues came
into play. In fact, I can't recall reading a single one, and like most
pilots, I eat 'em up to try and learn from others' mistakes. As I said,
the failure mode that matters most is failing to fly, or failing to get
out of ground effect.

If it is structural issues -- which I would suggest it very rarely is
-- you'll still have a huge safety margin when 5% or 10% over-weight.
You are not going to be getting that close to the 'g' envelope, and
your landings are hopefully not going to be hard enough to be given 10%
of collapsing the gear!

The answer to this is - it depends. I agree - the average flight does
not take you anywhere near the limits of the g-envelope. However,
momentary loads of 3 gees or more are not unheard of when flying in
moderate turbulence. So for a VFR flight under a stratus overcast,
sure, I wouldn't worry. For an IFR flight in cumuliform cloud, with
scattered embedded T-storms, I would reconsider. Note that while the
ultimate design load is 150% of the rated load, there is no requirement
for the structure to withstand the ultimate design load without damage.
Deformation is permissible. Repeated deformation due to excess loads
may be a problem. This all assumes the key structural components were
correctly manufactured in the first place, and have not deteriorated.
With an aging fleet, that may not be all that valid. However, I will
grant you that for a utility category aircraft, this is not an issue
worth considering.

The same issue comes up with regard to landings. Long smooth runway in
daylight and light winds, in a plane I've flown before many times? No
problem. Unfamiliar airplane and short strip with gusty crosswinds? I
think I want all the protection I can have. How tough is the gear,
anyway? When effectively the same gear is being used on an airplane
with a significantly higher gross weight, that tells you something (the
gear has plenty of margin). When you have a max landing weight lower
than the max takeoff weight, that tells you something too (the gear has
no margin - it is maxed out). Just something to think about.

Further, if you look at accident reports where over-weight operation
was a factor, I doubt you'll find many where structural issues came
into play. In fact, I can't recall reading a single one,

See the NTSB references in my reply to cwk.

Michael

The same issue comes up with regard to landings. Long
smooth runway in daylight and light winds, in a plane I've
flown before many times? No problem. Unfamiliar airplane
and short strip with gusty crosswinds? I think I want all
the protection I can have.

Agreed 100%. As I said before, it's about JUDGEMENT.

See the NTSB references in my reply to cwk.

I looked at these, both of which were for Cessna 402Cs, which I think
immediately says something about whether we're dealing with a general
or model-specific issue. The first, for N819BW, happened when the spar
broke where it had been subject to mechanical damage AND deep machining
marks. Hardly sounds like being over-weight was the cause here. The
second, N405MN, can't really be put down to anything, since very little
of the airplane was recovered. Again, hardly a clear case of
over-weight operation causing structural failure.