TUI B738 at Birmingham on Jul 21st 2020, female adults declared children, wrong takeoff mass computation

Last Update: April 8, 2021 / 12:02:30 GMT/Zulu time

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Incident Facts

Date of incident
Jul 21, 2020

Classification
Report

Flight number
BY-7226

Aircraft Registration
G-TAWG

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A TUI Airways Boeing 737-800, registration G-TAWG performing flight BY-7226 from Birmingham,EN (UK) to Palma Mallorca,SP (Spain) with 167 passengers and 6 crew, was preparing for departure when the crew noticed there was a mass discrepancy between loadsheet and the flight plan, that showed about 1606kg more takeoff mass than the load sheet. The crew felt content with the loadsheet, prepared their takeoff computation based on the loadsheet, departed and concluded a seemingly uneventful flight with a safe landing in Palma Mallorca.

The AAIB however determined, that the takeoff computation was wrong because a takeoff mass 1244kg below the actual takeoff mass was being used for that computation. All reference speeds should have been increased by one knot and a higher takeoff thrust should have been used.

The AAIB released their bulletin concluding the probable causes of the serious incident were:

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.

The AAIB provided following synopsis:

The operator had suspended operations for several months due to Covid-19 restrictions, and prior to the incident flight the reservation system from which the load sheet was produced had been upgraded. There was a fault in the system which, when a female passenger checked in for the flight and used or was given the title ‘Miss’, caused the system checked her in as a child. The system allocated them a child’s standard weight of 35 kg as opposed to the correct female standard weight of 69 kg. Consequently, with 38 females checked in incorrectly and misidentified as children, the G-TAWG takeoff mass from the load sheet was 1,244 kg below the actual mass of the aircraft.

Following this serious incident, the operator introduced a daily check to ensure adult females were referred to as Ms on the relevant documentation, with a secondary check by Operations staff against passenger loads. A more formal system of checks was introduced on 24 July 2020.

The AAIB also reported that on the previous day, on another aircraft, 3 adult females were checked in as children, on Jul 21st 2020 three more flights of the operator, one of them being the incident flight, departed with incorrect loadsheets.

The AAIB summarized the incident flight:

The aircraft was to depart on a scheduled flight from Birmingham International Airport to Palma de Mallorca airport (PMI), Spain. The weather at 0450 hrs, 10 minutes before departure, was wind calm, CAVOK, OAT 8°C, dew point 6°C and QNH 1026 hPa. As part of the prestart procedure, the flight crew reviewed the flight plan, which gave an expected takeoff weight (TOW) of 66,495 kg (Figure 1), and the load sheet, which gave a TOW of 64,889 kg (Figure 2). They noticed that there was a discrepancy, with the load sheet showing 1,606 kg less than the flight plan. They noted that the number of children shown on the load sheet was higher than expected, at 65, compared to the 29 which were expected on the flight plan. The commander recalled thinking that the number was high but plausible; he had experienced changing loads on the run-up to the temporary grounding as passengers cancelled and altered trips at short notice.

He remarked that variances between actual and expected Zero Fuel Weight (ZFW) were not uncommon. A further issue with the load sheet on the flight was the baggage load, which had been calculated as 35 bags at a standard mass of 16 kg, and 150 bags whose actual masses averaged 14.5 kg per bag. This was an unusual occurrence, but the use of actual masses was permitted by the Operations Manual. The commander also took care to check the load sheet taxi fuel was correct, as he had noticed a discrepancy with the flight plan statistical taxi fuel. After a brief discussion, the flight crew decided that they were content with the load sheet, the actual bag weights being very close to standard and the new ZFW being understood as a function of the differing passenger load.

The flight crew followed the normal procedure to calculate takeoff performance independently using the Boeing Onboard Performance Tool (OPT). With a light and variable wind, they elected to use a 5 kt tailwind with the load sheet data to compute takeoff performance. Nothing unusual was noticed by the crew on departure and the flight continued normally to the destination.

Subsequent use of the actual takeoff weight for performance calculations showed that all departure airspeeds should have been one knot greater than those used on the incident flight, and the thrust required should have been 88.9% N1 compared to the 88.3% N1 set on the incident flight. The screen displays from the Boeing OPT are shown in Figure 3, with the incorrect load sheet takeoff weight on the left and the correct takeoff weight on the right. The resulting one knot difference in takeoff speeds (V1, V2 and VR) can be seen in the bottom right of each screenshot, and the different takeoff thrusts on the bottom left.

A calculation was carried out for the actual TOW and environmental conditions, using a calm wind rather than assuming a 5 knot tailwind. The result showed that a thrust of 88.2% N1 would have been required to meet regulatory requirements.

The AAIB analysed:

The incident occurred due to a simple flaw in the programming of the IT system, which was due to the meaning of the title ‘Miss’ being interpreted by the system as a child and not an adult female. This was because in the country where the system was programmed, Miss is a child and Ms is an adult female. This issue had not been identified as part of the initial risk analysis and did not manifest itself during the trial simulations. For the incident flight, the weight of passengers on the load sheet was below the actual weight of the passengers by 1,244 kg, which was more than the 500 kg LMC weight difference above which a new load sheet should have been produced, had the weight discrepancy been identified.

When the issue was first identified, the operator had instigated Safety Action to prevent an incorrect load sheet being produced and used for aircraft performance planning. However, the work of correcting the adult females wrongly listed as children was handled by teams that were not working over the weekend. Passengers were able to check in online 24 hours before departure, on 20 July 2020. On this day, a software ‘fix’ was being applied to the system, possibly preventing it from identifying incorrect passenger status before the incident flight on 21 July.

Whilst an incorrect takeoff weight was used for aircraft performance planning, the thrust required for the actual TOW and environmental conditions (88.2% N1) was marginally less than the thrust used for the takeoff (88.3% N1). This meant the safe operation of the aircraft was not compromised.
Incident Facts

Date of incident
Jul 21, 2020

Classification
Report

Flight number
BY-7226

Aircraft Registration
G-TAWG

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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