CNN had an article which said that the FAA will ask airlines to weigh some passengers and bags before they board 19-seat planes to find out whether current weight estimates are accurate enough.
My immediate thought was "Ummm… why aren’t they weighting everything every single time? I know i wouldn’t want to be boarding a plane wondering if flying in a puddle jumper (20 passengers or less) with the front line of the Viking football offense was a bad idea.
What are the inherent technical difficulties in just weighing the whole plane once everything’s loaded? Would this be feasilbe at all, and if so is it prohibitivly expensive to set something like that up?
Oh, it isn’t technically challenging. Just put in a pad-style weigh scale like they have for weighing tractor-trailers beside the highway somewhere on the tarmac. There really isn’t that much point to doing it, though. Those 20 passenger turbojets are overengineered enough to handle a few extra tons, and you’re unlikely to be any further off the mark using estimates. Unless it is the Vikings chartering your plane, naturally, but then I’d think you’d just chuck the estimates and check out the roster.
Feasible? Sure. They do it for truck’s all the time. You’ve probably seen the weigh stations on the sides of numerous highways. Those trucks fully loaded can weigh 30 tons or more. I don’t see why weighing a puddle jumper should pose any problems.
That said you would need to install such weighing devices at airports all over the place which is likely to be quite expensive. Add to that the delays incurred by having planes roll onto the scale to be weighed not to mention the delays should something not be quite right and you’ve likely got a mess on your hands at the airport.
It sounds like they just want to revamp their estimates. I’m sure there is a large safety margin for those planes so unless you do in fact have the Viking’s defensive line on board you are likely just fine for most ‘average’ cross sections of passengers. They just want to be sure and see how the margins are growing or shrinking (likely shrinking).
Well, they may be over engineered to handle a few extra tons, but if the NTSB is saying that the Beech 1900 that crashed in Charlotte was within 100 pounds of that weight, then their estimates must be pretty far off.
And while it may be infrequent that you’d find yourself on a plane with the vikings defensive or offensive line ( I suppose the defense would be heavier, wouldn’t they?) the current estimates of 180.7 pounds for an “average” adult male doesn’t seem to fit anymore.
Heck… I’m fairly slim and I’m 190.
Either way you look at it, I was never fond of the idea of taking a puddle jumper and the idea that they are using an estimate to decide if the plane can take off or not isn’t soothing my fears.
Well, it depends on which weight they were within 100lbs of. Maximum recommended gross takeoff weight? Probably, in which case it’s no big deal. You can probably go 5-10% over that and have no troubles. Ever read stories about the early days of aviation with guys flying Ford Trimotors in the South Pacific? Or about WWII bombing missions at the edge of maximum range? They lifted off in birds that were overweight by a whole heck of a lot more than that.
If they were with 100lbs of the maximum weight the plane can theoretically take off at, then there’s more at issue here than FAA passenger weight estimates. Somebody would have to have been loading lead ingots into the luggage compartment or something.
I haven’t read the story on this crash, but based on what I know about aviation (no expert, but was an avid reader of related material for quite a while) I think the weight issue is probably a red herring.
Absolutely not true. Overloading any plane changes its flight characteristics so that takeoff distance, maneuvering and stall speed chages adversely. It’s not a matter of the wings falling off. It’s a matter of a plane going out of control from things like aft CG, augering in and then having the wings fall off.
You’d be suprised how thin the margins are on light aircraft for load. Two and four passenger aircraft often canot carry a large adult in every seat and a full load of fuel, let alone any baggage. Johnny L.A. can probably give you some specific figures.
The FAA plan is to weigh the passengers and cargo only, not the entire plane.
FYI, before any commercial airplane is certified by the FAA for flight, the airplane must be weighed first to determine the actual load limits to be placed on the aircraft. And this applies to everything from puddle jumpers to 747s. I saw the weighing of the first 777 that was going to be delivered for commercial use and it weighed within 60 pounds of the engineering estimate. The weight of the airplanes is a very serious matter to the customers and to the manufacturers, I am reminded of that every day at work with the posters hanging on walls in my shop at Boeing.
*The FAA plan is to weigh the passengers and cargo only, not the entire plane. *
Racer, yep… I read that in the article, which is what made me wonder why not weight the whole thing each time before take off?
I wasn’t thinking that the airplane itself was likely to be off the engineering estimate as much as I was thinking that estimating people and luggage makes me very nervous. Also, there’s the passenger issues with those times that they do weigh passengers and cargo in order to recalibrate their estimates.
I think there will be penty of people male and female reluctant to step onto a scale. If they want to board the plane they will have to do so, but it’s likely to ruffle some feathers.
That’s what generated the question… which I suppose could also be phrased as… is it easier to weigh the passengers, luggage, pilot, etc (i.e. variable weight factors) individually or just to weigh the whole thing once it’s loaded and ready to go?
And in that I’m thinking easier from both a technical and cost standpoint as well as a passenger perception and peace of mind standpoint.
I may not want the entire world to see my weight displayed on a scale before I board a plane, but I’d do that in a second realizing the saftey issue involved. But if I had the choice of flying an airline that required me to do that vs one that weighed the whole load once we’re already to taxi down the runway for takeoff… I’d take the second option. Less chance of someone mis-entering a weight somewhere.
The weight is only part of the problem. Where the center of gravity is at a particular loading is very important, also. Rolling the whole plane on a scale won’t tell you where the CG is.
The 100% best method is to weigh every item on the plane, take into account where the item is in reference to the datum on that aircraft, and calculate the weight and CG for every flight. I doubt that will ever happen for airliners.
Does the average 20-seat plane have much interaction with the ground crew normally? I’m thinking that if these plane normally just fuel up and take off, that adding an extra weight certification step on each take-off would be an rather extreme addition of time and expense.
I can address this part of the question. When loading a commercial jet it is assumed that passengers weigh a certain amount (165 pounds, I think). This pretty much averages out, especially as the capacity of the plane gets larger. A 747 with 400 people on it is a fairly random sample, so the assumed average works fairly well to calculate the weight and balance of the aircraft.
As mentioned previously, w & b is crucial to an airplane’s flight characteristics, whether the plane is large or small.
Some commercial jets are able to manipulate their center of gravity by shunting fuel around to different areas during flight. On the Concorde, for example, this is crucial for maintaining COG.
Another measure is to simply re-trim the plane, although that wouldn’t work for a COG grossly out of limits.
Quick story: A friend of mine used to fly charter in a Piper Navajo (8 seat twin prop). The owner of the plane weighed over 350 pounds, and on one flight had decided to sit in the rear with two friends. As the plane rotated at takeoff, the nose just kept coming up and wouldn’t stop, and the stall warning went off. My pilot friend yelled to the owner to move up front with such authority and urgency that he later remarked he had never seen 350 pounds move so fast.
Regarding passenger weights, realize that 180 lbs is used for EVERY passenger. This includes females. While I know most of my male friends are over 180 lbs by varying degrees, I know that most of my female friends are under 180 lbs as well. For most operations children are counted at 180 lbs as well.
Where I work, if the airplane is close to MTOW (Max TakeOff Weight) and we have a full load of passengers they will do a child count: physically count the number of children on board, and re-calculate the passenger weight based on this. Each child is assumed to weigh 90 lbs - it may not seem like a lot, but say out of 120 passengers 15 are children - right there you save 1410 pounds. The system is built to assume on the “fat” side, if you will - all women and children weigh 180 lbs.
Also, variations are made for time of year (extra weight is assumed in winter for clothing), where you are flying (each passenger is 160 lbs coming out of Japan) and for baggage (something crazy like 210 lbs per passenger coming out of Haiti).
These calculations have been fine-tuned over the years and work reasonably well. The only time that weight and CG problems become safety-of-flight problems is usually with a loading foul-up - either data is entered wrong or the wrong cargo is loaded in the wrong place.
If the FAA wants to update the passenger weight assumptions (because Americans have gotten fatter, obviously), they will not be having everyone stroll onto a scale at the gate and be subject to ridicule. They will gather enough data (by weighing volunteers privately, maybe) until they have a large enough statistical database and then issue a new “average” passenger weight.
As I said, in scheduled air carrier operations this is not that big of a deal. The higher the gross weight of the airplane, the less each individual passenger affects its flying performance. Small single-engine airplanes can be greatly affected by the addition of a single passenger. On a 757 that same passenger and his entire family could go unnoticed performance-wise.
To finish, I agree with Gorsnak that the weight issue is a red herring. The NTSB needs to (and should) check into the weights of the accident airplane, but I’m looking at the elevator as the cause of the crash myself.
For a 1985 Cessna 172P Skyhawk the standard empty weight is 1,433 pounds. Maximum takeoff weight is 2,407 pounds. That leaves a useful load of 974 pounds. Total standard fuel is 43 gallons, or 258 pounds. That leaves 716 pounds for the passengers and baggage: 179 pounds each for four people and their baggage. Not so bad for two adults and two children plus a bit of baggage. But what if you have four 200-pounders? Either one will have to be left on the ramp, or you’ll need to offload some fuel. Got options? A nice full IFR panel, maybe a GPS or weather radar? Air conditioning? (Okay, I haven’t seen a 172 with radar or air conditioning, but it could happen.) Those are added to the weight of the airplane and subtracted from the useful load.
But wait! There’s more! You also have to take in the centre of gravity (CG). Not only must the aircraft not be overloaded, but the load must be distributed. If the CG is too far forward you may not have enough elevator authority to pull out of a dive. If the CG is too far aft, you may not have the elevator authority to put the nose down to avoid an aerodynamic stall. It gets worse with a helicopter, where you not only have to figure longitudinal CG but alst lateral.
Of course Broomstick is more experienced than I am, so she can give us more information.
Just roll the front wheels on to the scale, check the weight, then roll the main gear on and weigh it again. You could figure out the center of gravity from the two readings[sup]*[/sup]. Truckers do the same thing, they not only have overall weight limits, but maximum weights per axle.
pilot141, I saw in another thread that you used to fly Starlifters. My Dad used to fly those, I think they’ve just about phased them out by now.
[sub]* You’d need some specs on the airplane, position of the landing gear and reference datum, but you’d need something like that for any system of this sort.[/sub]
You’re required to have certain documents in addition to your pilot and medical certificates to operate an aircraft in the U.S.
Airworthiness certificate Registration Radio station license* Operating limitations (the POH) Weight and Balance information
[sub]* I’m not sure if this is still required. I thought I heard about a change a few years ago. When I fly, all of those certificates are with the aircraft.[/sub]
Sure, but that’s even more of a pain than just weighing the people and running a normal W&B.
It would be neat to have three scales embedded in the ramp, spaced correctly for a Beech 1900. As the airplane taxied over them, a display on the side of the taxiway would light up with the takeoff weight and CG. I would be running my 172 over them at airports just for the fun of it.
On preview, the radio license isn’t required in the US anymore.
You may have a different operating handbook than I do (and it’s been a few years since I’ve flown), but mine had the moment arms for front seat, back seat, fuel tank, etc. If the data for landing gear position was in there, I don’t remember seeing it. Now that I think about it, fore/aft CG limit probably reduces down to maximum/minimum of the main-gear/nose-gear weight ratio.
Joey, do you think weighing all the passengers (and knowing their seat numbers, assuming they don’t move around) and knowing the weight and position of all the baggage is more of a pain in the ass than just stopping twice on the taxiway?
Considering the safety record, I don’t think anything like this is really necessary. And it would probably be a huge headache in practice. (For one thing, they’d probably want to space the scales so they could be used on more than just a Beech 1900.) Yes, there are truck scales by the sides of highways, but I can’t remember the last time I saw one that was open and working.
What I was getting at is that the seats, etc. have distance from the datum line published in the POH. Fill out a weight-and-balance worksheet and come up with the numbers, then look on the weight-and-balance charts that are also published in the POH. By knowing how much weight you’re putting on the aircraft and where you put it, there is no need to weigh the whole aircraft and calculate the CG from the gear weights. Just look it up on the chart.
I think that in a large aircraft such as a Beech 1900 that passenger weight estimates are good enough. They should all average out.
Anecdote: My mom is five feet tall and weighs about 110. Her husband is about six-foot-seven and weighs about 270. They had to take a commuter plane (I don’t remember what kind – maybe a Beech, and maybe a Cessna) to get to their destination. They said that for W&B reasons my mom had could sit in back; but her husband “had to” (“We’re very sorry.”) sit in the right seat. (This is why I think it was an eight-passenger Cessna.) I put quotation marks around “had to” because both my mom and her husband were pilots, so it was really no hardship for my mom’s husband to sit up front. He lost his medical several years ago, so it was as close as he could get to operating an airplane again.
As far as the passengers moving around, commuter flights are generally short and there’s only one head. There’s not much opportunity to move about, so I think that is a very small worry.
And, yes; I agree that the safety record is exemplary and there is no need to institute such rules. Unfortunately the sheeple feel that “someone should do something”, which can result in onerous rules that really don’t do anything. (“But if it saves just one life…” “Won’t someone think of the children?” :rolleyes: *)
[sub]* Not to belittle safety, which is a very important thing. It’s just that we can’t make the world an entirely safe place, and we need to accept some risk when undertaking most endeavors.[/sub]
