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Whose responsibility is accuracy of W&B?

Cardiff Kook

Cardiff Kook

PATRON
Sisters, OR
Newbie here.

I've been looking at a bunch of late mode planes for purchase and reading through log books.

On a number of planes the weight provided does not match w&b.

I recently noticed the W&B on a plane which was based on equipment added/removed did not match the equipment currently installed. There are items which would significantly (20 pounds+) change weight. Props. Tires. Etc. Bear in mind this is not an old aircraft so it's not like 80 years of mods.

I look through logs but never considered "is this w&b correct?"

How do you protect against this? Is this liability from passed to new owner? I know most say "don't put a plane on a scale" but I don't want to absorb someone else's liability.

Planes in question have limited useful load and I am trying to stay legal.



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91.103 - Pre Flight Action- the Pilot In Command Shall . . .

91.417 - Maintenance Records - the Owner or Operator shall keep the following records

43.9 each person who performs maintenance, preventive maintenance, rebuilds or alters an aircraft shall make a record entry

In short, the person that makes changes is responsible to make the appropriate entry, the owner or operator is responsible for seeing that those entries are done, and the pilot in command is responsible for checking before flight that they have been done.


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What dgapilot said.

Now, what makes you say the "propeller" for instance, on that plane, wasn't on that airplane the last time it was weighed? Is there a logbook entry for the installation of the prop, but no notation of a change in W/B? Could it be that that prop was identical in weight to the one replaced?

The point being, it may take some digging to really figure out what the "correct" weight is. That said, the weight and balance report has a mechanic's signature on it (or it should). If anything was added or removed since that certificate was signed, the plane isn't legal.....that is, permanently installed equipment....portable GPS is not "installed".

MTV
 
If you really want to stay legal, weigh the plane, just be prepared for the truth!! The key to buying airplanes is to find a good IA and listen to what he/she says about the plane. Most small planes will fly over gross weight without problems (happens every day) the key is the where is the CG. DENNY
 
In simpler terms, here's what the FAA W&B Handbook says. The mechanic or repairman is responsible for keeping the W&B current, which implies accurate. Some are better at it than others.

Responsibility for Weight and Balance
Control
The responsibility for proper weight and balance control
begins with the engineers and designers and extends to the
technicians who maintain the aircraft and the pilots who
operate them. Modern aircraft are engineered utilizing stateof-the-art technology and materials to achieve maximum
reliability and performance for the intended category. As
much care and expertise must be exercised in operating
and maintaining these efficient aircraft as was taken in their
design and manufacturing:
1. The designers of an aircraft set the maximum weight
based on the amount of lift the wings or rotors can
provide under the operational conditions for which
the aircraft is designed. The structural strength of the
aircraft also limits the maximum weight the aircraft
can safely carry. The designers carefully determine
the ideal center of gravity (CG) and calculate the
maximum allowable deviation from this specific
location.
2. The manufacturer provides the aircraft operator with
the empty weight of the aircraft and the location of its
empty weight center of gravity (EWCG) at the time
the certified aircraft leaves the factory. Amateur-built
aircraft must have this information determined and
available at the time of certification
3. The FAA-certificated mechanic or repairman who
maintains the aircraft keeps the weight and balance
records current, recording any changes that have been
made because of repairs or alterations.
4. The pilot in command (PIC) has the responsibility
prior to every flight to know the maximum allowable
weight of the aircraft and its CG limits. This allows
the pilot to determine during the preflight inspection
that the aircraft is loaded so that the CG is within the
allowable limits.
Click to expand...
 
I rarely encounter "correct" Cub weight & balance documentation. Worse on Super Cubs, but problematic on all older light planes.

Most mechanics are not well schooled in such things - they are better at fixing stuff than at paperwork. Buy an aircraft that you like and fix the computation errors.

If somebody has weighed a Cub and placed it in the 1PLM category, look carefully to see if it can legally be returned to two place. A local Cub has the empty weight noted on about six 337s - no way that aircraft will ever return to two place without stripping all the mods and going back to factory weight.
If you insist on weighing, keep the numbers on the W/B sheet, and resist the temptation to file them in OKC.

Opinion.
 
Thanks, all.

One issue for me is the planes I am looking at are S-LSA. I believe there is a 890 lb empty weight cap or you are no longer legal- forget about gross.

Most of the planes are a few pounds from that number...
 
When a mechanic makes a change to the equipment, it's his responsibility to make an entry showing the change to the W&B. However, the accuracy of his entry depends completely on the accuracy of the previous entries. Math errors, especially using negative and positive numbers are very common here. And planes put on weight as they age due not only to equipment changes, but grunge under the floorboards, small items added by the pilot, etc. It all adds up. Ultimately, it's the pilot's responsibility to ensure the plane is being flown within the W&B limits. As previously mentioned, they fly over gross all the time, but getting outside of the CG limits puts you into a bad mode of test piloting. It's rare that I ever weigh a plane that comes within 100# of what the W&B paperwork says it weighs, and they are almost always significantly more.

-Cub Builder
 
Cardiff Kook said:
Thanks, all.

One issue for me is the planes I am looking at are S-LSA. I believe there is a 890 lb empty weight cap or you are no longer legal- forget about gross.

Most of the planes are a few pounds from that number...
Click to expand...

There is no empty weight limitation for a Light Sport aircraft (unless specifically identified by the manufacturer). The only limitation is gross weight. Of course, when the empty weight goes up, the useful load goes down. That's what often makes a single place airplane out of a two place airplane.
 
As others have stated, when a change to the aircraft occurs, the mechanic is responsible to update the W&B and Equipment List. Unfortunately, the Equipment List is most often neglected. Recognize that it is the OWNER that should be holding the mechanic to provide the proper documentation. Every airplane I've owned lacked a "current" Equipment List, and as the OWNER., it was my responsibility under 91.417 to update it, and as the PILOT, it was my responsibility to be sure it was available under 91.103.

Now, the OP is concerned with an S-LSA airplane, and that gets even more sticky as that airplane can't have any alterations unless the manufacturer authorizes those alterations. I hate S-LSA airplanes, even as a mechanic, our hands are tied to only being able to do functions listed in the aircraft manual. I think the concept of S-LSA is the worst thing to happen to general aviation!
 
Plus 1 on the first paragraph. No experience with S-LSA except flying a Legend, so cannot comment. Dave is an asset here.
 
I'm glad this thread came up. It caused me to look hard at my old logbooks and documents from the the disc I ordered from the FAA.

Learned a lot: Like, the manufacturer of my Commonwealth in 1946 calculated the initial cg wrong. The weight and balance sheet shows he subtracted the distance from the datum (leading edge) to the mains instead of adding. That left a cg that was 1"+ ahead of the Operation Limitations sheet.

Then he happily used that wrong cg moment arm to calculate everything else. It was driving me batty to see all the cgs for different loadings forward of the 10.3" to 18.2" range specified.

So I ran the numbers myself using the reported scale weights and moment arms of the mains and tailwheel, and everything was fine.

Then I went back and added (instead of subtracting) the distance between the leading edge and the mains, and got the same numbers from his chart.

There is no operating handbook or envelope diagram. Instead there are 4 scenarios of weight and balance calculated for reference. The funny thing is that they all have the right numbers.

Additions and removal of equipment was haphazardly logged, but I have the benefit of a 2007 weighing entry with current equipment. Unfortunately, my bird has gained almost 80 pounds from when it was built. Now I have a useful load of my wife, me, and maybe two sandwiches at full fuel.

Which is OK. At least we are in the proper cg range.
 
I have seen quite a few logs where mechanic swapped equipment, tires, pods etc. and didn't revise the W&B or equipment list. I find and correct. One was from the manufacturer from the start. They used one arm from the actual measurement and another from the datum. It had been modified from wheels, amphib floats and back, 3-4 different props, fuel pod and several other mods over the previous 15 or so years including some flight testing.
 
If / when you end up buying an airplane,
if you have any doubts about the W&B being accurate (or even if you don't),
I'd suggest you re-weigh it and make up a new W&B report.
Be sure & level the airplane correctly, as per the TCDS,
and also use a plumb bob & tape measure to measure the arm of the wheels & the datum (also per the TCDS).
The W&B on my 180 was right on the money when I got it,
but that wasn't the case with the two airplanes that I owned before that.
 
I have always suspected the old factory scales. As Dave says above, weigh a Cub or an old Aeronca, and gain 100#. That is a lot on a 725 lb airplane!

Weigh a 180 or a 7ECA, and you come within five pounds of factory/computed weight. Whatever it is, it isn't just dirt in the belly that adds 100 lb to a stock J3.
 
Last time I weighed a PA-11's complete fabric covering it was close to 80# when removed. Randolph-Ceconite I believe but may be wrong. I wonder how much the original cotton-linen-nitrate-whatever covering in the 1940-50's weighed? More or less?

Gary
 
Probably less because they were skimping on dope and labor. But not 100 pounds less! Modern, glossy finishes probably add 30 lbs. That's a guess - I have heard that 65 lbs is a good number for fabric and dope.
 
I have the original factory W&B booklet that came with our Super Cruiser. It is amazing what is listed as options! Pretty much everything! Rumor has it when they were weighing Cubs that was done "in the silver" before finishes. I expect very few of these 1947 factory booklets
Have ever survived the decades. IMG_20211007_204633543.jpgIMG_20211007_204529795.jpgIMG_20211007_090148857_BURST000_COVER.jpg
 

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Local friend had one of those "As Weighed 951" PA-12's. Never gained a pound despite the full electric, O-320 with metal 74" prop. Plus some gauges and radios during a few recover jobs since new. "Weight added negligible" has different meaning to different folks.

Gary
 
Interesting. 951. My Commonwealth has the exact same empty weight when it left the factory. Hmmm.....
 
A lot of what I've found over the years, especially with somewhat larger aircraft than Cubs, such as 206, and even more so in twins... Entries that will say something to the effect of "removed ADF" or removed Autopilot, or some other older tube type radio, and then you get to looking and they basically cut the wires and took the head out of the panel and called it removed....leaving the heavy part or servo's and almost always the old wiring still in the aircraft....then they look in the manual and it'll say "weight 4#", so they use that on their weight and balance paperwork. I've more than once seen a 10+ pound pile of wiring and old tube trays, etc, laying on the floor, after the complete removal of a few of these old installations.
As far as who's responsibility...I was always told ultimately it's the PIC, but if I just signed the inspection, and it's obviously in error, I'm going to be on the hot seat as well... just like an AD.
John
 
Gary,
This one has gained lots of weight over the years, however it was completely restored in 2000 and a new W/B was done on digital scales and like all the rest of em it too has
Gained nearly 100 lbs.......
E
 
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Another mechanic on the field is doing an annual on a freshly painted aircraft and says it should have been reweighed. I have never heard that before. Strip, prime and paint. We will see where he goes with it.

I did a bunch of weight saving mods on a Super Cub years ago and then weighed it and it weighed more than the W&B said. Customer wasn't happy.
 
My Cessna’s factory reported weight was a fantasy. No way it weighed as little as they said.

About 15 years ago my mechanic insisted on having it weighed and a new equipment list made. The reported weight did go up. Not a big deal, it is what it is. I’ve weighed it a couple of times since, primarily after I changed the interior and panel. Scales don’t lie. Pilots do.
 
The factory paperwork on my first airplane (1969 C150) showed the weight of the paint job--
I don't recall the exact number, but it wasn't insignificant.
Early C180's came from the factory polished with minimal trim.
Again, I don't know the exact numbers, but the full paint job on most of them (including my 53 model) adds a lot of weight.
Most mods do also, take mine for example:
K engine, 88" prop, 185 gear legs, 850's with double-pucks, 10" tailwheel, steps & handles, extended baggage, pull handles.
Unfortunately about the only mods that reduce weight are the Odyssey battery, the BAS jumpseats,
and the Garmin G5 instead of a vacuum system & gyros.
 
Just for fun look at these two Type Certificates. Particularly TC #639 Look at the added weight of the different paint colors. It varies from no weight change with aluminum to +51 pounds with French Grey.
https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/92ae1915586208dc8525673f005d1a56/$FILE/ATC597.pdf
https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/bf98e6d0fae5df048525673f005d1696/$FILE/ATC639.pdf
 
Recall that Don Sheldon reportedly stripped his Cessna's for performance; that included the paint. It was significant enough to do apparently. If repainted a new W&B might be in order.

Gary
 
My reference was taking a painted aircraft into a paint shop where the old paint was completely stripped and the aircraft was repainted. Sure there could be a change in weight but in reality paint off, paint on. I see no reason to reweigh.
 
Same paint likely no need. Change product or coating then maybe. I'm not adverse to reality - the cost of weighing is how much? Last one I did was $200 but that changes.

Gary
 
When I worked in a paint shop we always weighed after as well as balanced surfaces as applicable. I'd definitely expect it if I had an aircraft painted.
John
 
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