Smart Useful Load Margins

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rksmith81

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rksmith81
Greetings all,
I’m a new private pilot purchasing an older aircraft and useful load is a topic I’ve been giving serious consideration to. In particular, deciding on and allowing for safe margins when considering that I’m purchasing an aircraft manufactured in 1988. What do you guys think are realistic and safe margins? Useful load is 1,265 lbs. Is capping my personal limit at 1,000 lbs being to conservative?
 
rksmith81 said:
Greetings all,
I’m a new private pilot purchasing an older aircraft and useful load is a topic I’ve been giving serious consideration to. In particular, deciding on and allowing for safe margins when considering that I’m purchasing an aircraft manufactured in 1988. What do you guys think are realistic and safe margins? Useful load is 1,265 lbs. Is capping my personal limit at 1,000 lbs being to conservative?
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You’re attacking this the opposite way most people do. Rather than capping useful load, you should cap the excess runway available after doing the performance calculations with whatever your actual weight is.

even 265 pounds light, you will have a fixed runway length needed, so you have to do the math anyway.

It’s far less about structural capability and more about performance, and a hot day / high density altitude can ruin your performance more than adding 265 pounds can.
 
That's a lot of useful! What plane?
 
Unless I am flying in mountains or real short runways, I don't have any issue flying all the way up to max gross. In mountains I max out at 90% MTOW.
 
I’ve never done it, but I’ve heard of planes taking off a couple hundred pounds over gross!
 
rksmith81 said:
Greetings all,
I’m a new private pilot purchasing an older aircraft and useful load is a topic I’ve been giving serious consideration to. In particular, deciding on and allowing for safe margins when considering that I’m purchasing an aircraft manufactured in 1988. What do you guys think are realistic and safe margins? Useful load is 1,265 lbs. Is capping my personal limit at 1,000 lbs being to conservative?
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Think of it this way - the manufacturer already built in a safety margin - you don't need to further limit yourself. A "little" out of CG is riskier than a "little" over gross - I think someone once figured out a 100 lbs over gross raises the stall speed on a 172 by one knot. It's likely your engine doesn't go back to 1988, either. And by then POH performance graphs were pretty accurate - for sure give yourself more runway than the graph minimums, and BELIEVE in the effects of hih density altitude.
 
When was the airplane last weighed ,so you will have an accurate number to work with. The figures from the manufacturer have a safety factor built in. It’s more about being able to meet the climb gradient to clear a fifty foot obstacle.
 
The margins are already built in. As long as you are within the envelope, you are good to go.
 
When I used to fly fractional ownership, our manual said we could use any of the three options:

1) Standard weights
2) Actual weights as measured at boarding
3) Passenger stated weights, plus 10 lbs per passenger

IMO that is good enough.
 
Learn the airplane. If you’re new to it you need to get some seat time in it.
 
I believe that people take off over gross more often than most people think. Let’s say you’re in a Baron, which has a 5,400 max gross. You fill the tanks, cabin and baggage hold to a couple hundred pounds over gross with plenty of runway. It burns 12 or 13 gallons per side or something like that. Say 25 GPH. You will burn off that weight in less than an hour and the plane was less than 4% overweight at takeoff.

The reason I picked the above scenario is remembering of an ill fated flight three or four years ago. A very experienced ATP pilot left from the Houston area in a B58, that was full of very rotund individuals, bound for Kerrville which was a short distance for a Baron. Due to the weight, the pilot elected to take off with enough fuel to make Kerrville. It probably would have worked except he experienced a wind and weather change that forced him to go past Kerrville to shoot an approach from the other direction rather than his original plan of flying straight in. He ran the tanks dry and everyone perished.

This accident brings many issues into mind. First of all, he apparently didn’t have his destination plus 30 or 45 minutes. I don’t know if he had filed or not. Secondly, it points out that the plane can fly overloaded, but it can not fly without fuel, at least not very far.

I am NOT proposing that any of us fly over max gross. I AM pointing out the tragic mistake of leaving behind adequate fuel instead of letting Aunt Margaret or the baggage stay behind, or even flying a little over gross, can be a dead serious decision.
 
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MBDiagMan said:
I believe that people take off over gross more often than most people think. Let’s say you’re in a Baron, which has a 5,400 max gross. You fill the tanks, cabin and baggage hold to a couple hundred pounds over gross with plenty of runway. It burns 12 or 13 gallons per side or something like that. Say 25 GPH. You will burn off that weight in less than an hour and the plane was less than 4% overweight at takeoff.

The reason I picked the above scenario is remembering of an ill fated flight three or four years ago. A very experienced ATP pilot left from the Houston area in a B58, that was full of very rotund individuals, bound for Kerrville which was a short distance for a Baron. Due to the weight, the pilot elected to take off with enough fuel to make Kerrville. It probably would have worked except he experienced a wind and weather change that forced him to go past Kerrville to shoot an approach from the other direction rather than his original plan of flying straight in. He ran the tanks dry and everyone perished.

This accident brings many issues into mind. First of all, he apparently didn’t have his destination plus 30 or 45 minutes. I don’t know if he had filed or not. Secondly, it points out that the plane can fly overloaded, but it can not fly without fuel, at least not very far.

I am NOT proposing that any of us fly over max gross. I AM pointing out the tragic mistake of leaving behind adequate fuel instead of letting Aunt Margaret or the baggage stay behind, or even flying a little over gross, can be a dead serious decision.
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If you tie dinky to the strut you don’t have to count him against your useful.
 
Maybe the pilot of the Baron going to Kerrville couldn’t find a strut on the Baron where he could tie Dinky.
 
I fly a 78 C182 at gross weight all the time. Get some training flying at gross weight and at front & back cg locations. There is nothing wrong with limiting your useful load until you get some time in the airplane. I would not limit the useful load based on the age of the aircraft.
 
My only change is during the summer here in Texas we fill the Warrior to the tabs rather than chock full just as a matter of practice for a slight performance improvement in the heat…otherwise no issue flying at gross as designed.
 
Flying near gross is fine if you follow the POH.
The differences that are very obvious are:
- with two rear passengers, the CG is further back, so the trimming will be very different (much further forward)
- the climb rate will be noticeably reduced, so careful on short runways with obstacles at the end
 
great point on rear CG above.. I'm often at or near max gross, and the rear loading is what gets me nervous. I have, more than once, had backpacks and heavier things on the floor by the rear seat pax. Also like the point above about padding weights 10lb. The Aztec has a nose compartment so that makes it easier, but the twinkie does not

People lie about their weight, so guess heavy, or, if they tell you, add 10lb. Keep in mind people don't fly naked and shoes, phone, wallet, bottle of water, headset, all that misc crap adds up
 
rksmith81 said:
Greetings all,
I’m a new private pilot purchasing an older aircraft and useful load is a topic I’ve been giving serious consideration to. In particular, deciding on and allowing for safe margins when considering that I’m purchasing an aircraft manufactured in 1988. What do you guys think are realistic and safe margins? Useful load is 1,265 lbs. Is capping my personal limit at 1,000 lbs being to conservative?
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A plan made in 1988 isn't old. Age has nothing to do with the useful load. If the plane is in good shape, and you don't overstress it by exceeding the operating envelope, you will be fine. If you're worried that the plane might not be in good condition because of its age, that's a problem that should be rectified with inspections and any needed repairs, not artificially limiting operations. If you're worried that you might not have accurate empty weights because of age and accretion, then have it weighed.
 
Personally, I don't like that weight and balance get lumped together.

Flying at gross is not nearly as exciting as flying at the rear balance limit. 20 lb over weight is not the same as 2" behind the rear limit.

Balance is a more important to thing to worry about.
 
jbarrass said:
Personally, I don't like that weight and balance get lumped together.

Flying at gross is not nearly as exciting as flying at the rear balance limit. 20 lb over weight is not the same as 2" behind the rear limit.

Balance is a more important to thing to worry about.
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Gross means nothing. However, Performance is very nearly as important as cg, and you need to know your weight to know your performance.
 
Under some conditions, FAR §91.323 allows for a 15% increase in max gross weight in Alaska. To include airplanes a lot older than year group 1988. CG is the thing I pay more attention to, as that more directly influences handling characteristics.
 
That weight allowance only applies to 121 and 135 operators and the change has to be approved by FSDO.

My planes' performance can be plotted on a curve. While light loads performance is stunning and mid weight performance is quite good, the performance curve falls off sharply approaching gross weight and gets worse over gross. Performance changes are particularly evident in rate of climb and slow speed control. At or over gross the landing speeds need to be higher than normal and you may discover that your braking power is not as effective with the added weight, let alone added speed, so landing distances get a double dose of performance decline.
 
Kritchlow said:
When I used to fly fractional ownership, our manual said we could use any of the three options:

1) Standard weights
2) Actual weights as measured at boarding
3) Passenger stated weights, plus 10 lbs per passenger (BUT NEVER SAY THAT OUTLOUD - IF WIFE, DON'T ASK AT ALL)

IMO that is good enough.
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Added some important safety information to your fine post.......
 
I am surprised at how many people are basically say flying at gross without pointing out that it really depends on the circumstances. I'm hardly a weight weeny, but I think the ability to recognize scenarios and adapt to scenarios that require careful consideration is the real question, e.g. high DA, short runways, complicated terrain on climbout, wind across ridges/mountains, etc.
 
I’d be much more concerned w/being outside CG than gross weight. You can be under gross and outside CG and wishing you’d never left the ground.
 
MBDiagMan said:
The reason I picked the above scenario is remembering of an ill fated flight three or four years ago. A very experienced ATP pilot left from the Houston area in a B58, that was full of very rotund individuals, bound for Kerrville which was a short distance for a Baron. Due to the weight, the pilot elected to take off with enough fuel to make Kerrville. It probably would have worked except he experienced a wind and weather change that forced him to go past Kerrville to shoot an approach from the other direction rather than his original plan of flying straight in. He ran the tanks dry and everyone perished.
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I believe this is the accident you are referring to. A lot of little mistakes made for a horrible outcome:

 
AA5Bman said:
I am surprised at how many people are basically say flying at gross without pointing out that it really depends on the circumstances. I'm hardly a weight weeny, but I think the ability to recognize scenarios and adapt to scenarios that require careful consideration is the real question, e.g. high DA, short runways, complicated terrain on climbout, wind across ridges/mountains, etc.
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I think it’s been stated enough times here to be covered. ;)

But since the OP’s question wasn’t about performance (and doesn’t give enough information to make performance assumptions), it would be appropriate to answer it directly without performance references.
 
FWIW, max gross is not always based on flight performance. The FAR or CAR used for certification basis will specify other factors involved in computation.

For instance, my 8KCAB has a MGW of 1800 pounds. This is based on a drop test which measures how much the gear deflects when dropped from a specified height, to prevent prop strikes due to bad landings. When the aircraft was recertified with longer gear legs, the MGW was increased to 1950 pounds. Updating a metal-winged aircraft with the new gear legs gets the new MGW.

At current MGW of 1800 pounds, my airplane climbs like a scalded monkey.
 
Some people say if it fits it flies, weight and balance already is pretty conservative and is a safe number. There are exceptions for exceeding weight and balance so the plane does still fly (see the US to Hawaii flight in a C172 that had a W&B waiver for the excess fuel needed). If it’s a hot day, high altitude or high density altitude, you’ll need more runway, you wouldn’t want to take off on a short runway or have obstacles to overcome if your W&B and density altitude are both high. Know your CG whether it’s forward or aft and the characteristics of each and Know your airplane too!
 
Daleandee said:
I believe this is the accident you are referring to. A lot of little mistakes made for a horrible outcome:
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Yep, that’s the one. There were several issues involved, but if he had added fuel, it is highly likely that he would have gotten by with it. It’s a good lesson for all of us.
 
I'm curious about all the comments about aft CG being a bigger problem than gross weight. Pireps?
 
I frequently fly the Cherokee at gross weight. I try to avoid it in the summer or when out west at higher elevations but even then, I sometimes do it if I know the airport and I have enough runway length. Just be aware of the terrible climb performance but if no obstacles are ahead and the runway is long enough, nothing wrong with flying at gross weight. Having said that, I don’t ever go over gross weight knowingly. I carry a scale with me and weight all bags all the time. However, my mechanic told me today that when he cleaned my plane after the annual, he cleaned off a good 10 lbs of dirt. In theory, that means every time I was at gross weight, I was actually 10 lbs but manufacturers build this type of margin error into their numbers.
 
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