Weight and Balance: How Much Do You Weigh, Miss?
A number of airlines suspended operations during the worst of the pandemic that has disrupted the world over the past year. One of these, a British charter airline owned by a German-Anglo travel and tourism company, were in the process of upgrading their systems, including their reservation software, when the pandemic hit.
The integrated check-in system allowed passengers to check in twenty-four hours before departure and used their information for various paperwork, including generating the load sheet for the flight. The load sheet documents the weight and balance for the flight, listing the weight of the aircraft, the crew, fuel, passengers, and any baggage and cargo. This information is used to calculate the aircraft’s take-off performance, for example what thrust will be required for take-off and the V-speeds.
Passenger weights are done as an estimate, based on an average weight. Most airlines differentiate between adults and children. In the UK, the Civil Aviation Authority requires separate weights for men and women.
Because a correct load sheet is so critically important, there are a number of checks and balances in place to ensure that the load sheet is both correctly calculated and that it reflects reality.
Training meetings for the upgraded software took place in February 2020 and the software worked as expected. Passengers select their own titles when checking in and in the meetings, the titles available were checked against standard usage as set by the International Air Transport Association.
There was no further discussion documented in the training session about what effect the titles had, other than cosmetic.
Flights were resumed on the 10th of July. On the first flight after the upgrade had been put into service, the flight dispatcher noticed something wrong: an adult female passenger had been marked by the check-in system as a child and the load sheet added her weight as 35 kg, instead of the estimated weight for an adult female of 69 kg (77 pounds instead of 152). It turned out that as a part of the upgrade, an error had been introduced into the software, in which any passenger using the title Miss was marked as a child.
They found that two more adult women on the flight had used the title Miss and both were added to the load sheet as children. The load sheet was fixed and the problem escalated.
The report does not mention where the system software was written, other than to clarify that in that country, the equivalent title to Miss is used for a child and Ms for an adult female. Certainly in modern German, I would only use Fräulein for a child or teenager, with Frau for any adult woman, without regard to her marital status.
This was the system that the upgraded software used, with the result that all adults using the title Miss were logged as a child and added to the load sheet at 35kg, almost half the weight of an adult woman.
A fast response was needed, as the software would need changing and testing and rolling out.
The operator set up a team to look at all upcoming bookings and changing all adult females with the title of Miss to Ms, which avoided the issue. As an ongoing fix, two teams were assigned the task of checking bookings every afternoon and evening for the next day’s flights to ensure that adult women were not logged as children by the system. Where possible, flights were checked again on the day of departure.
Check-in staff were also asked to watch for female passengers at check-in and boarding and verify that they showed in the system as adults.
The fast fix, from a software point of view, was to automate what the two teams were doing: change the title of all adult females from Miss to Ms, which was implemented on the 17th of July. However, this fix could only modify passenger information before check-in. Any passengers already checked in were not amended, for example those who checked in online up to 24 hours before the flight.
The teams doing the manual checks did not work over the weekend after the software fix was implemented.
The software was modified again on the Monday 20th of July. There’s no clear information as to whether that stopped the program from working or somehow reset it. That day, online check-in was opened early for flights on the 21st. Female passengers checking in as Miss did not have their status or weight corrected.
On the 21st of July, the day after these modifications, three flights departed the UK with incorrect load sheets. The first of these, G-TAWG, was a Boeing 737-800 on a 5am scheduled flight from Birmingham International to Palma de Mallorca airport in Spain.
That morning, the flight crew reviewed the documentation for the flight. The flight plan gave an expected take-off weight of 66,889 kilograms while the load sheet stated that the actual take-off weight was 64,889 kg, a discrepancy of 1,606 kg or 3,540 pounds.
The flight crew noticed that the load sheet showed 65 children on board as opposed to the 29 which were expected. This seemed high but plausible and explained the difference in weight. As travel restrictions were changing rapidly in July, the captain said he’d noticed loads changing more often than usual as passengers cancelled and scheduled flights at short notice.
He said that it was not uncommon for the expected Zero Fuel Weight (the weight of the aircraft including crew, passengers and cargo) and the actual Zero Fuel Weight to be different.
Another oddity was that the cargo was calculated as 35 bags at a standard measurement of 16kg each and 150 bags whose actual mass averaged 14.5 kg per bag. This was unusual but the Operations Manual was clear that actual mass could be used.
There were thirty-eight adult women on the flight who had been incorrectly estimated at weighing 35 kg each. The actual discrepency was 1,244 kilograms less than the actual weight.
The wind was light and variable. The flight crew selected a five knot tail wind to calculate take-off performance using the load sheet data, which showed their weight as 1,606 kg less than it should have been. This had the following effect:
- The take-off thrust was calculated as 88.3% and should have been 88.9%
- The departure airspeeds (V1, VR and V2) were one knot less than they should have been.
Entering the tailwind helped: when the same calculation was done using the actual take-off weight and a calm wind, as was the weather at take-off, the thrust required was 88.2% N.
The aircraft took off normally and the crew did not notice anything unusual as they departed Birmingham.
The AAIB released the Serious Incident Report this week:
A flaw in the IT system used by the operator to produce the load sheet, meant that an incorrect takeoff weight was passed to the flight crew. As a result, the aircraft departed with
a takeoff weight 1,244 kg more than stated on the load sheet. An upgrade of the system
producing load sheets was carried out to prevent reoccurrence.
When this was discovered, the pilot and the operator filed an Aircraft Accident Report Form. They reinstated the process of manually checking all flights daily to ensure that the title Miss was amended to Ms when used by adult female passengers with a secondary check by Operations staff. They also gave a reminder briefing to Ground Handling agents to watch for adult female passengers showing as Miss or as a child at check in. A formal procedure for a Customer Care Executive, which appears to be a classy term for customer service representative, to check all bookings was put into place on the 24th.
The airline have made a quiet statement on the issue:
The health and safety of our customers and crew is always our primary concern. Following this isolated incident, we corrected a fault identified in our IT system. As stated in the report, the safe operation of the flight was not compromised.
All in all, rather a non-incident which could have been handled better. I found it interesting, how a minor cultural issue can have such an unexpected result. Next week, I’ll post about another case where the take-off weight was calculated incorrectly, this one with fatal consequences, although, of course, that wasn’t the only thing that was wrong.