I’m reviewing an NTSB report for an airplane crash and I came upon this sentence:
In this incident, the aircraft was essentially destroyed and all flammable cargo and passengers were destroyed by the post-crash fire. How could they possibly determine the center of gravity, or that it was 500lbs over gross weight? The wreckage couldn’t have yielded this information, and I have to think that the pilot wouldn’t have logged this information and then knowingly attempted an overweight takeoff with family onboard.
I could accept that there wasn’t enough evidence to determine the cause of the accident, but I knew this pilot and I can’t believe he would have taken off overweight, and I can’t see how the investigator could reliably determine an aft center of gravity from the destroyed wreckage. It really smells like they contrived a narrative to fit the available video evidence (pitch back and stall immediately after takeoff, followed by a roll and inverted dive into terrain).
Surely they knew who the passengers were. And there was probably some understanding of the cargo–if it’s luggage, etc., they can interview the families to get an idea of how much there was. Along with knowing the fuel load of the craft.
Given that, along with some inferences about where the passengers sat, the CoG can also be computed.
Care to give some more information, a link to the accident report maybe? I assume that this was a small aircraft. Many will be significantly overweight with just an adult in every seat and full fuel. They’d have all that information.
Do you have a link to the report? It will help to know the aircraft type and some other details.
As for weight, they know what the aircraft weighed and they’ll look at logs, past trips, and even fuel records to determine what fuel was onboard. The load weights might be a bit of an estimate but pretty accurate as you’ll know the passengers and can estimate what they had for luggage.
From there it’s simple calculations of weight and balance. And pilots do dumb stuff all the time, that’s why there are accidents.
I have a hard time buying it. Cessna P210N is known for having a wide CG, I’m told that it’s hard to overload it aft, and it was fueled for an 800 mile trip with the tanks fore of CG. He could have made some other mistake, I was thinking he might have taken off trimmed for landing, but I don’t see how he would have risked taking off overweight and tail-heavy in this aircraft, and also not locked his seat. He was known to be a thorough and conscientious guy, I have a hard time seeing him be so careless with the kids onboard.
If you look on the last page of the accident report, there is this link: NTSB Docket - Docket Management System
which contains a link to the full NTSB weight and balance report.
The calculation is based on fuel (~1000lb), the 4 adults on board (average-sized), and what looks like 33+80 pounds of luggage.
The issues that I see are:
I think the pilot probably filled up with more fuel than needed because he’s used to flying alone or with two people on board when it’s not an issue.
I think with 4 people you would usually not use the aft seats, but one of the middle seats had a 33lb bag on it, and one 171lb passenger was in an aft seat. And a heavy 80lb bag was aft.
The passengers would have been 620lb max. Minus 480lbs fuel, that’s 419lbs luggage, which doesn’t seem to fit for 2 kids and 2 adults on a 3-day trip.
As I said he could have made mistakes, he was new to the aircraft, but weight and CG just doesn’t make sense to me.
It wasn’t 4 adults, it was 2 adults and 2 young teenagers. I don’t know the fuel information but if we assume the 480lbs figure from @DrStrangelove then it doesn’t add up, not even close.
Riemann’s link is a good one. It shows a total fuel load of 992 lbs. 596 from full main tanks, plus 179 from a transfer (tube?) and 217 from tip tanks. I based the 480 lbs on 80 gal (since the plane is specced for 900 nm with 90 gal). Obviously that was an underestimate.
Well, I think your estimate may have been closer to what was actually needed for the trip. I suspect that the pilot was just used to filling it up (when there were fewer people on board) and it just didn’t occur to him that you can’t do that with 4 on board.
The airplane was about 14% overweight and would have needed a little more nose down pressure or trim to compensate. Someone who flies can tell more about how that would affect the flight. It may have aggravated the situation but I don’t think the NTSB saw it as the reason for the accident.
From the NTSB report:
The pilot’s failure to ensure that his seat was properly secured before initiating the takeoff, which resulted in a loss of control during the initial climb. Contributing to the accident was the lack of an installed secondary seat stop, and the airplane’s aft center of gravity condition.
My interpretation is that on takeoff, as the aircraft’s nose raised, the pilot’s seat slid back because it wasn’t properly secured or the seat stop failed. A service bulletin had been issued for that type aircraft because the seats had failed in the past, and the pilot had complied with one of the bulletins but not the other requiring a second stop.
Seat slides back and the pilot, surprised and hanging on to the stick as he slid, pulled the nose up resulting in the stall. The fact he was already a bit tail heavy just aggravated the situation. At that altitude, he had no time to react to the failure.
He wasn’t used to anything, he had just bought it and hadn’t flown it more than 2 hours. It was his first turboprop. I could understand if he made mistakes regarding handling or performance, it’s just hard to believe that he fucked up basic math with the kids onboard. He was known to be careful and thorough, very much a numbers guy.
Yeah, plus that aircraft had both tip tanks and a transfer tank installed, which aren’t on the base model (and don’t seem to be mentioned in the basic report).
Whether or not he was used to this type, most private pilots do most of their flying with 1 or 2 people on board, and by default just fill it up. With 1 or 2 pob occupying the front seats, weight & balance is never an issue.
Pilot made a major error with the weight and balance - even if there’s some uncertainty in the NTSB figures, it’s not as though it’s even close to being within limits. It’s clear that he didn’t do the calculation at all. He didn’t need all that fuel, so there was no point in risking being overweight. And the C of G could have been improved considerably by just putting the 171lb adult in the other front seat, the two teenagers in the middle seats, and the 80lb of luggage on the rear seats rather than the aft hold.
I appreciate what you’re saying but this gets back to my basic question, the aircraft impacted terrain nosedown and all passengers and cargo were consumed by the ensuing fire. How can we even suspect the spatial distribution of the cargo and passengers?
What makes you believe that the aircraft was so thoroughly destroyed that they could not tell who was in which row of seats?
I know it’s not what you want to hear, but all the evidence points to the pilot just not having done the weight and balance calculation at all, a mistake that’s easy to make when you don’t need to bother to do it for 95% of your flights.
The seat positions were known, and could be recovered even from a significant fire. The location of the fuel tanks are obviously known. The only extra part was an 80 lb bag in aft storage (which actually had a pretty significant contribution to the CoG). I’m sure they had some means of verifying the existence of that. Oh, and a 33 lb bag or something strapped to one of the seats.