Loading luggage, passengers and CoG

[Cralis]

Does the flight crew know where the centre of gravity is just before departure? Is that trust in the loading crew? Or does the aircraft indicate the CoG, maybe using weights from the nose wheel and main gear?

I know the FMC indicates the trim setting based on fuel and loads of other factors. That trim setting would be pretty accurate, you'd hope.

Would it just be unlucky is the CoG was far back, and that wouldn't effect performance, as you can fix it by moving fuel around?

Could it become an issue?

[DaveReidUK]

Originally Posted by Cralis

I know the FMC indicates the trim setting based on fuel and loads of other factors. That trim setting would be pretty accurate, you'd hope.

The FMC can only work out the aircraft's weight and balance if it's given accurate information about the OEW and the distribution of pax, bags and cargo.

GIGO applies as much here as it does anywhere else.

[rog747]

the ground guys should be conscious of loading and CogG of different types

examples
some a/c had tail props attached during loading such as dash 7 and sh360 (also dc 8 and 707 747 freighters)

707 freighters you loaded a heavy pallet in Posn A first if you could before sending the others down the back
757 load the forward 10 rows of pax first if all or most of the bags were going in the rear hold

that sort of thing

[Elephant and Castle]

CoG for Take off, Landing and Zero fuel weight are in the load sheet that is reviewed by both pilots and signed by the captain. On occasion the CoG is very near or over the limits and the capt will ask for a redistribution of pax or cargo.

[eckhard]

For large passenger jets operating for big airlines, there is a 'Dispatcher' or 'Turn-round Manager' (TRM) whose function is to co-ordinate all the ground processes prior to departure.

The TRM will have access to the aircraft's basic weight and CG schedule and will input the expected passenger load, baggage, freight and fuel figures. This will produce a 'provisional load-sheet' showing the forecast Zero Fuel Weight (ZFW) Taxi Weight, Take-Off Weight (TOW) and Landing Weight. It will also show the ZFW CG and the TOW CG. These last two are normally expressed as as a percentage of Mean Aerodynamic Chord (MAC) rather than a distance from a fixed datum.

The flight crew use the provisional figures and the ATIS data to load the FMC and to calculate take-off thrust and speeds. The FMC may provide some of these figures but it is a case of GIGO as others have mentioned. Eventually all passengers and freight are loaded and the TRM is in a position to finalise the figures. These may vary from those forecast due to missing/extra passengers, changes in the number of freight pallets loaded, etc. At some point before take-off, the final figures are passed to the flight crew in the form of a 'final load-sheet'. This may occur prior to doors closed or else during the taxi-out.

The flight crew review the final figures and check whether or not they differ from the provisional figures by more than a pre-determined percentage or figure. If the final figures are within the tolerance, there is no need to adjust anything and the take-off is accomplished as planned. If however the final figures differ by more than the allowed tolerance, the FMC must be partially reloaded and the take-off performance recalculated.

The FMC may run its own 'reasonable' check of the entered figures and may show a warning message if it detects a gross error. Some aircraft are fitted with pressure or extension sensors on the gear which may be used to accomplish this cross-check.

[Cralis]

Thanks very much, guys. That's really helpful and enlightening. I'm not scared of flying, but that's the bit I always worry about most - have they got it right. Is the nose going to come up too much unexpectedly due to a missing decimal point. But it seems there's enough checks to mitigate that.

Thanks.

[Johnny F@rt Pants]

Having said all that, we are all human, and unfortunately, very occasionally, they get it wrong.

[KelvinD]

Sometimes they get it right and ignore it. Waiting to fly from Frankfurt to Lisbon in the early 90s, I watched from the gate as a 30 minute battle to load a large wooden crate into the forward hold of "my flight", a 737. Eventually they gave up and managed to shove in the aft hold. After we had all boarded, doors closed etc, the pilot got on the PA and announced they had some trouble loading cargo etc and, for the take off, could we all please move forward temporarily to help balance the aircraft and we could return to our assigned seats when we had got some altitude. I ended up in the front row and had a great view of the take off run as the cockpit door had popped open. I was a bit surprised when the aircraft did a bit of a slalom just prior to lifting off. Not long after the take off, we were asked to retain out temporary seats for a while longer. The engines went to idle and we started a long slow descent on our route, with the wheels down. The FO came out of his seat and wandered up and down the cabin with a small torch, peering out of the windows. By the time we reached Luxembourg, it was wheels up, power up and a climb to the right altitude to cross Paris. We were told that the aircraft had hit an animal on the take off run at Frankfurt and the FO was checking for damage and we could all now resume our assigned seating. A long way out of Lisbon, the engines went to idle, the wheels came out and a long slow and winding descent into Lisbon began. We were asked to all move forward again. When we landed, the aircraft came to a sudden stop on the runway. It was then taxied onto an exit and stopped again. The pilot explained to us he thought something had been damaged and we had to wait for ground staff to come out to examine the landing gear. It was then announced one of the left main wheels had been "destroyed" and we had to be towed to the gate. What did we hit on the runway that caused this damage? A rabbit!
However, back to the main point; this flight departed with the C of G so far out they had to shuffle all the SLF forward to redress this!

[surely not]

KelvinD the fact they shuffled the pax forward for take off and landing means that they had allowed for the change in C of G for take off and landing, so it didn't depart with 'a C of G so far out'.

Load sheets are designed to allow for the loading to be planned, and re-planned if necessary, in a way that keeps the aircraft within the trim envelope for that particular type of aircraft and that is safe for the flight. During the flight testing to gain an aircraft certification the flight trim envelope is fully explored and airlines operate within the results of these tests.
Each aircraft type will have an optimum trim range that gives the best payload/range for the type, however there will be times when this isn't achievable, so a less optimum, but perfectly safe, trim is agreed on.

[Kewbick]

It is all about moment-arms. When you fly a Beech-Raytheon 1900D, for example, it is preferable to seat the heavier passengers to the forward of the C-of-G than aft. Why? First of all, the baggage compartment is in the extreme aft of the aircraft. Secondly, you don't want to rotate tail-heavy which may result in a stall. Better to not rotate at all, or have substantial resistance to rotation. Thirdly, the Beech 1900D's nose wheel retracts rearwards, pushing the C-of-G aft at a critical time.
Sample example with a single-engine Cessna:

[pax britanica]

Of course moving pax around was more of an issue on the tail engine jets when it was quite common if the aircraft was lightly loaded to have it filled up from the front.
There is also the all people are not the same factor which kicked in ona flight i took from LHR to Frankfurt on a long LH321. I and my two colleagues were in the very last row and a cc comes back and asks if the three people in front us can move forward for weight and balance reasons

All east Asian and around 5 ft in height they count have weighed much. the three of us on the other hand still in the back row would make a decent rugby front row with a combined weight of about 50 stone ( about 320Kg) so I doubt moving the girls made any material difference to the Cof G at all.

Also flew on a BAe146 along with the Toulouse rugby team/squad , bit of a difference in weight between them and the standard pax weight, some of them were literally gigantic - assuming the gate staff knew who was on the plane would they try and seat the big guys as close to Cof G as possible?


There is an old story of a flight leaving -in fact nearly not leaving - somewhere because of Cof G issues as it had a lot of people up front who were valuable coin collectors and effectively had carry on s full of gold.

[MATELO]

@Kelvin

I watched from the gate as a 30 minute battle to load a large wooden crate into the forward hold of "my flight", a 737

I stood and watched a shorts 330 I was due to fly Newcastle/Belfast on being loaded with what seemed like a million bags, a whole rugby teams kit and caboodle. These were stowed in "the boot" and I dare say the pilots were professional, but it felt like they were just saying "yeah, chuck it on, we'll be ok". Got me thinking a little bit of the weight in the back on rotation as we seemed to hang for a couple of seconds just after getting airborne.

[Out Of Trim]

Just to allay some misconceptions; the final load-sheet is usually completed by a Load Controller, with any major changes incorporated within. It is a legal document that cannot be produced without all C of G and weight limits being complied with.

At times, though passengers and or baggage may have to be moved to achieve this prior to departure.

[KelvinD]

In the 1990s, the ex and I spent some time on the island of Boracay (Philippines), before it became over-exploited. The flight from Manila was a tiny aircraft with room for 3 passengers. The return flight was on a larger aircraft and I have no idea what it was. I remember it was a twin engine tail dragger with something like 15 to 20 seats arranged along the fuselage, facing across the cabin. When we checked in for the flight, baggage was weighed on a big old fashioned set of industrial scales. As we were boarding the aircraft, a couple of blokes in tee shirts, shorts and flip flops were loading the baggage. The baggage was stowed in the cabin, on the floor, in between the 2 rows of passengers. Once all was loaded, the 2 baggage handlers climbed over the baggage, donned sun glasses and settled down in the driving seats! We were taking off toward the NE which was a bit worrying as the airport then had a hill at that end, with the sea immediately beyond that. After lifting off, the pilot seemed to put the aircraft into a steep climb until we had cleared the hill, then into a shallow dive, presumably to get some air speed back. A bit like driving over a hump back bridge. I had to stop myself from shouting "Wheee"! Half the passengers were either crying or screaming, including a lady sat opposite me who never stopped praying and crossing herself for the entire trip! I have never been so glad to get off an aircraft. As I say, I have no idea what the plane was but from the seat belts I could see it had been a Pan Am aircraft once upon a time. The abiding memory of that trip was watching the crew climb over the mound of baggage along the cabin floor!

[dixi188]

DC-3 I should think.

[DaveReidUK]

Originally Posted by dixi188

DC-3 I should think.

That was my first thought, too, until I got to the part about side-facing seats.

[KelvinD]

Dave, that is exactly the seating arrangement on that flight. So that was a DC3? It seemed a bit smaller than the only other one I have been inside; the BBMF model at Coningsby. If you can imagine the space between the boots in the photo being covered in baggage and the pilots clambering over it .....

[b1lanc]

Originally Posted by Elephant and Castle

CoG for Take off, Landing and Zero fuel weight are in the load sheet that is reviewed by both pilots and signed by the captain. On occasion the CoG is very near or over the limits and the capt will ask for a redistribution of pax or cargo.

Happened to me at Stapleton on a 737-200. Less than half full of pax but after engine start we sat. One very very large pax was moved from the main cabin to first class. Crew announced CoG issue and after pax move, off we went.