How do you determine what a "safe" overweight condition is?

[Hocky]

I'm talking about the gross weight of the plane not an obese pilot.

I've seen articles where people who are ferrying planes over long distances get some kind of waiver to take off way over the maximum gross weight for that plane.

How is that determined?

 

[Jim Logajan]

I'm talking about the gross weight of the plane not an obese pilot.

I've seen articles where people who are ferrying planes over long distances get some kind of waiver to take off way over the maximum gross weight for that plane.

How is that determined?

See page 4-111 "4166. Special Flight Permit for Operation of Overweight Aircraft." in this document, which goes into extensive detail:

http://www.faa.gov/documentLibrary/media/Order/8130.2G .pdf

 

[Jim Logajan]

Something that puzzles me: Most of us here take max gross weight seriously. And yet, I've seen plenty of comments about highway speed limits being low or stupid or whatever, and where I live, at least, most people speed. And there are some awesome speed-related accidents. Why the disconnect?

The amount of risk appears to increase as a continuous function with increasing road speed, while the laws of physics create a discontinuous function of risk with increasing gross weight of airplanes. So in the case of road speeds the risk increases smoothly enough that no one speed stands out as the best place to set the limit. With airplane gross weight there are obvious points where there are distinct inflection points. Other than safety factors, over which one may debate, the failure points are quite distinct.

The following web page has a simple formula for speed/crash risk and more than you or I care to know about how speed limits are set:

Methods and Practices for Setting Speed Limits: An Informational Report
http://safety.fhwa.dot.gov/speedmgt/ref_mats/fhwasa12004/

 

[Jim Logajan]

In Alaska you can fly over gross.

Section 91.323 does not allow flying over gross. That section appears to only provide for what is essentially a re-certification at a higher maximum weight in limited circumstances. And it is not an automatic re-certification.

 

[Jim Logajan]

Can anyone point me to an NTSB report of any 172 folding up in flight short of going into a large thunderstorm? There are many out there that have over 10K hours, been beat mercilessly their whole lives by students, been flown overweight, etc. There are many here operating 50 year old aircraft of all types that have been through who knows what and we don't have them folding up in flight.

There are many more important things to worry about.

Lots to choose from; here is a sample:

http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20071218X01970&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20130227X70316&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20100215X82210&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20070111X00045&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20030325X00386&key=1

Sample of accidents where flying over gross was causal though not so much as to cause the wings to fold up:
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20110814X60630&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20130428X00603&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20120527X21141&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20110815X10520&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20110528X21434&key=1
http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20100602X45201&key=1

This one isn't a Cessna, but is rather infamous:

 

[Jim Logajan]

First one doesn't count (spatial disorientation pilot got the plane sideways)
Second one doesn't count (pilot lost his vision WTF and got the plane sideways)
Third one doesn't count (bad modification)
Fourth one doesn't count (spatial disorientation pilot got the plane sideways)
Fifth one doesn't count (pilot dove straight down again WTF)

So how about a case where an overloaded 172 failed a structure in normal flight. No spatial disorientation, no going blind, no attempt to face plant the plane?

Those were normal flights - up until they became abnormal.

The NTSB listed over gross as causal in the other 6 accidents you failed to address. And those 6 were just a subset of the accidents I found meeting the over gross criteria and on point with respect to the question posed in the thread's subject line. One reason it is difficult to find accidents where over gross conditions cause structural failure is probably because the excess weight causes the accident very early - generally during takeoff.

 

[Jim Logajan]

I would only do it with acceptable density altitudes, long runways and no hard bumps.

Given complete (or near complete) knowledge of the future forces and environment that the airplane would be exposed to, then of course one can reduce the safety factors while not increasing the risk. So long as the future plays out as expected, you're good. In general the FAA doesn't think you have enough knowledge of the future to change those safety factors - unless you can show otherwise in some official manner.

But setting up a scenario where the foresight is near perfect doesn't establish anything you or anyone else didn't already realize prior to you posing the question in post 1.

I'm sure everyone is sick to death of this thread.

Not me. I see threads like this as great vehicles for everyone to learn something - whether related to safety or how to handle themselves on online forums. The lessons may not sink in today, or tomorrow, but soon, and for the rest of your life.

Lucy van Pelt: Adversity builds character. Without adversity a person could never mature and face up to all of the things in life!
Charlie Brown: What things?
Lucy: More adversity!