Air TransportLATAM 777-300ER tail-strike in Milan traced to 100-ton take-off weight error
Italian investigators have concluded that a 100-tonne error in take-off weight calculations led to a tail-strike involving a LATAM Boeing 777-300ER during departure from Milan Malpensa in July 2024, an event later reclassified from a serious incident to an accident due to the extent of the damage.
The aircraft, registered PT-MUG, was departing runway 35L for São Paulo when the tail contacted the runway shortly after rotation. According to the final findings released by Italy’s accident investigation authority, ANSV, the crew used incorrect take-off performance data after miscalculating the aircraft’s gross take-off weight.
The cockpit crew consisted of a captain undergoing line training in the left seat, a line-training captain in the right seat, and a cruise captain. The final loadsheet was received about 10 minutes before pushback. While the correct zero-fuel weight was entered into the flight-management computer, the line-training captain made an error while mentally calculating the gross take-off weight.
By subtracting the expected taxi fuel consumption from the displayed gross weight, the captain arrived at a figure of 228.8 tonnes instead of the correct 328.4 tonnes. Investigators said the incorrect value was spoken aloud, leading both pilots to enter the same wrong figure into their electronic flight bags for take-off performance calculations.
Because both flight bags were based on the same erroneous input, the cross-check between them showed matching results, masking the mistake. ANSV noted that no comparison was made with the final loadsheet or with the data stored in the flight-management computer.
The incorrect weight led to unsuitable configuration and assumed temperature settings. As a result, the flight-management computer was unable to generate a valid take-off solution within the available runway length, triggering a “V-speeds unavailable” message. Although all three pilots noticed the alert and discussed it, the investigation found that the crew did not identify its cause or stop the departure.
Investigators pointed out that the calculated speeds were significantly lower than expected for a fully loaded 777-300ER. Correct data would have produced V1 and rotation speeds in the region of 172kt and 181kt, but the crew used values of about 145kt and 149kt.
During the take-off roll, rotation was initiated at around 150kt, roughly 30kt below the required speed. At the same time, the incorrect assumed temperature setting meant the GE Aerospace GE90 engines were not producing sufficient thrust.
Four seconds after rotation began, the aircraft reached a pitch attitude of 8.3° nose-up. At about 160kt, the tail-strike protection system was active, but the tail still contacted the runway. By then, the aircraft had exceeded the calculated decision speed, making a rejected take-off no longer feasible, even though that speed itself was based on incorrect data.
With the aircraft not responding as expected, the cruise captain intervened and ordered full take-off thrust 12 seconds after rotation began. The engines reached maximum thrust shortly afterward, and the aircraft lifted off at 178kt with approximately 800 m of runway remaining. A positive climb was established, and the 777 crossed the threshold of the opposite-direction runway 18R at about 155 ft.
After completing initial checklists, the crew declared urgency, dumped 72 tonnes of fuel, and returned to land safely on runway 35R. None of the 398 occupants was injured.
Initial inspections found damage to the tail-skid assembly, drain mast, and the auxiliary power unit fire-extinguishing system. Subsequent detailed inspections identified additional structural damage, prompting ANSV to reclassify the occurrence as an accident. The aircraft returned to service around seven months later, after repairs and further checks.
ANSV said the event showed how a single calculation error, combined with incomplete cross-checking and misinterpretation of cockpit alerts, can escalate into a high-risk situation even when aircraft systems are functioning as designed.
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Creator of the website that started in 1996 as a magazine. He also writes on Brazilian websites AUTOO, MOTOO and MetrôCPTM.
