Southwest Airlines suddenly grounds scores of planes due to aircraft weight issues
 

How does this happen and what the heck does it really mean?

"Southwest Airlines abruptly grounded 66 Boeing 737 aircraft in its fleet last Wednesday after issues with the carrier’s aircraft weight records were discovered.
In an internal memo to employees on the matter that was obtained by the Chicago Business Journal, Southwest said: “Today (Wednesday) we discovered the weights being sent to our Dispatch Operation did not match our other weight records for a number of aircraft in the fleet. As a result, and out of an abundance of caution, we have stopped flying those aircraft to recalculate the weights of the aircraft in question and reset the program.”
Aircraft weight is important because dispatch personnel and pilots need the correct information to determine the amount of fuel to load and other data needed to safely operate a flight."

https://www.bizjournals.com/chicago/...hoo&yptr=yahoo

Erm, go with the higher weight from the two sources and operate with reduced passengers loads until the data issue is resolved? Any safety reports to suggest this is a serious airworthiness issue?

Mnnh - SWA, particulary with regards to aircraft records, is getting "the fisheye" from the FAA at the moment. As well as a lawsuit, both stemming from the fatal engine explosion near Philly. A time to make sure all the i's are dotted and t's crossed.

And the backstory is, the FAA itself is getting some flak and oversight (IG investigation) for perhaps being too "chummy" with operators.

"An abundance of caution," as the memo states.

As to how it happens - weight may "accrete" on an air frame, as things like passenger wi-fi, or even flight systems, get added or upgraded (or even removed). And maybe not all departments "get the memo" of the change to aircraft N000SW's weight, so the records don't match. Big corporate bureaucracy (or perhaps too small and overworked a corporate bureaucracy).

It's possible the higher of the 2 weights may also be incorrect.

Sensible to ground the aircraft as a precaution imho.

Some things never change. Shortly after the Decmeber 1, 1974, TWA 514 CFIT, TWA's POI was transferred. Rumor had it that he was too chummy with TWA's flight ops management.

either it meets the FARs or not, "chummy" has nothing to do with it, except for how long it was out.

Of course the bigger issue is what went wrong in the process at SW end..

...with the merger between Southwest and airTran, airTran had 66+ B737-700's in their fleet.

Lomapaseo

Well, "chummy" can mean the local FAA guy him(her)self doesn't cross-reference all the weights on file: in the onboard W&B paperwork; in the airframe's FMS; in dispatch's paperwork; in the maintenance records; in the master file at HQ. Never assume that even "good guys" can't get a little lax, now and then, trusting the operator's processes because they are also "good guys/gals."

I'm not knocking either the FAA or SWA (for whom the fatal event was their first (onboard, aircraft failure) in 51 years) particularly - human mistakes can creep in anywhere. You catch 'em, you tighten ship.

Is this related to the issue of fleet weights discussed recently in Tech Log?
changing registration on Loadsheet....

Legally you are not allowed to despatch an aircraft without knowing the correct weight. As they cannot determine which record is correct, if any, then they had no other option.

Classic example of the 'Normalisation of Deviance'. Best to stop because, irrespective of the laws quoted above, losing a single pax life is not good for anyone.

Its not only the weights, the weight document from technical services will also indicate the centre of gravity (basic index) which the starting point to calculate the aircraft CG and have %MAC.

Underfire - I'm pretty much with you. Gallup reports that U.S. men self-reported weights that averaged out to 191 lbs (women, 159 lbs). One may think that even those are low (due to vanity) but the same groups reported that their ideal weight would be about 20 lbs less (they were honest enough to admit they were a bit - chubby). 25% of men admitted to 200+ lbs; 29% of women admitted to 175-200+ lbs.

So the FAA numbers are about right - IF one excludes clothes and carryons, and only counts flesh. And 20 pounds shy with those added (in my case, the real extra weights are below the assumptions most of the time, if not, sadly, the body weight ;) I weighed my winter overcoat - 3 lbs)

OTOH, let's take, oh, a nice average 737-800 with 2-class seating. 160 people plus babes-in-arms and crew = 180 x 20 = 3600 lb error. Given a MTOW for the 738 of 174,200 lbs, that is a 2% error. 157 feet/50 m on a nominal MTOW takeoff run, negligible in terms of exceeding MTOW unless one habitually flies with full tanks.

Redo the math as needed, for an Islander or an A380.

Nevertheless, I'm all for some updated statistics from which to "average."

This is the most interesting and potentially apposite comment so far. Perhaps Air Tran methods/standards were different and when put into the SWA system the calculations did not work. A simple ontological problem could cause that if there is no Boeing standard.

Of which SWA inherited 52, I believe, so that doesn't account for all of the 66 grounded 737s.

Did we not have a discussion on here a couple of years ago about the Irish VLCC ' gaining advantage ' by registering some / all its fleet with lower gross weights in order to benefit from lower En Route Charges from Eurocontrol ?

Something similar at Southwest, perhaps ?

Really? They did it on purpose to "gain an advantage" with 66 out of over 700 of their aircraft and then suddenly changed their mind and grounded those aircraft? Excuse me if I sound a bit incredulous.

haha.. double my weight !

It was just a thought about the ex-AirTran aircraft....

I think the discussion about the Irish VLCC was something along the lines of as long as they were flying comparatively shorter stage lengths and so were rarely carrying full fuel then it could be that the aircraft never departed at the manufacturer's MTOW....Or something like that....

But as I said, just a thought...

.

Interested PAX here. I always wondered what the average figures for calculating passenger weight are. Is that a global standard?

Or maybe had to relocate a few to accommodate mini horses as service animals as announced today.....

In the USA it's 190 pounds in the summer and 195 in the winter. There are separate male/female numbers of 200/205 and 179/184 but everyone I know just uses the average. Children up to 12 are 82/87 but most times they are just counted at 190/195 also. Sometimes when trying to carry a jumpseating crewmember on a weight restricted flight I've heard Captains asking if any of the pax are children. Two kinder would allow the jumpseater.

No idea if the numbers are standard around the world. The FAA raised the numbers several years ago after a Beech 1900 crash in CLT. They said they would monitor American weights and adjust as necessary.

There is another European LCC who does/did this. Not sure about a previous discussion, but they registered lower Max weights for the fleet. The weight of the aircraft was what it weighed but the max payload was reduced. From memory, the structural limit was around 71T, one group reduced to around 64T, another to around 62.5T and some more to around 60.5T. No idea of the saving it generated but with large fleets, even small amounts will help and go straight to the bottom line.

A few years back one of the UK locos ran an exercise to check the accuracy of their weights. Aircraft were weighed in the hangar during maintenance to verify actual weight against the recorded figures and also selected at random as they entered the apron after a flight and directed onto a stand equipped with pressure pads. They were marshalled carefully onto the three pads and after about a minute, if even that, were able to disembark pax normally. Results were correlated with the flight papaerwork and processed.

Results showd the standard weights used were remarkably good, iirc something like a 2-300Kg deviation from the paper figure which on a 60t aeroplane is extremely accurate.

Southwest 737 Short Grounding in September
 

Temporary grounding of 115 737-800 at Southwest took place due to weight difference of 75lbs in IT vs. actual mass. Took some days until half of the fleet returned to service. Reported to be a difference <0.05% of MTOW.

from aero international magazine

Safety matters, but isn't this a bit surprising?

This works primarily in Europe, where landing fees and Eurocontrol charges are all driven by a MTOW based formula. In the US these charges are per movement or category based, so playing with the weight figures for a given aircraft model has no effect on operating costs.

Would it not make sense for the flight crew to complete their own weight and balance calculation using an EFB or similar device? This way the airline can ensure that they have up to date records of their own fleet weights without having to worry about disseminating the information to all of their handling agents and auditing it. The handling agent present a loading form with passenger weights, distribution and load in compartments for the flight crew to enter into their own EFB. Similar devices are used for computing takeoff performance, surely adding a WB function wouldn't be too difficult?

And its not just in Europe. The AFM will likely show 70,999 or 71,999 for instance. This is not an unusual occurrence.
On the Airbus, you have multiple WVs.

Here are the numbers for Canada. Note that the adult weights in the table include a 13 lb allowance for carry-on:

https://cimg9.ibsrv.net/gimg/pprune....6342b9b58c.png

https://tc.canada.ca/en/aviation/ref...-ac-no-700-022

andrasz

Had some 727s at an old job, exNW airframe converted freighters, the landing weight had purposely been lowered to reduce the landing fee paid. We sent a check to Boeing and in a few weeks had new placards raising the max landing weight 4000 pounds.

I remember several years back taking a co-worker to the airport for a flight to Sydney on a very small airline. Earlier that year they had experienced a fatal crash. One thing I had never seen before was weighing each passenger and when everyone was checked in, assigning seats. Second was that the pilot got a fuel sample from the fueling truck, took it into a back room, and after a few minutes came out and gave the fueler the okay to proceed. Too bad it took a crash to tidy things up.

It's hard to imagine taking 66 jets abruptly off the line when as many available jets are roosting in the sun at VCV, plus the now recertified 34 Max jets.

txl No here is not a global standard; there are 'regulator' standards and should an airline choose to do so, they can seek approval for their own standard passenger and baggage weights. There is a strict process and mathematical model behind the derivation of the standard weights published, used and approved. Typically they are derived from a study of real passengers (actually weighing many hundreds if not thousands across a population at the aircraft side, including all hand baggage) and the numbers run through standardisation methodologies with a confidence interval of 98%. Meaning that the average weights applied for Male, Female, Child and Infant (including hand baggage) is accurate to within +/- 1%. Same for those that use a standard, as opposed to actual, baggage weight for mass and balance calculations prior to a flight departure.