Argentinean investigators have found that a Flybondi Boeing 737-800 was out of balance before it tipped up and struck its tail while attempting to depart from Iguazu Falls airport last year.
The aircraft had just commenced its take-off roll from runway 31 when, about 6s after its thrust levers were advanced, it abruptly pitched up at about 30kt, causing its aft fuselage to scrape the ground. Its crew aborted the departure and returned to the parking stand.
Argentinean investigation authority JIAAC says the aircraft was transporting 65 passengers and a crew of six on a service to El Palomar at night on 16 July 2018.
Budget airline Flybondi had acquired the aircraft (LV-HQY) three months earlier, in April, after it came off lease with Turkish Airlines as TC-JGH.
It had been configured with 165 economy seats for the Turkish carrier but it was refitted in France with 189 economy seats for Flybondi.
Airport handling documentation was updated, as required, to reflect the aircraft' new weight-and-balance envelope under the new seating layout, says JIAAC.
The load and trim sheet for the flight lists the passengers as being distributed primarily in the front of the aircraft, with 38 in the two forward cabin sections and 27 in the two aft sections. This put the calculated centre-of-gravity at 22.2% of the mean aerodynamic chord.
But JIAAC says the actual distribution "did not correspond" to that prepared on the sheet. All but a few passengers were located in the two aft sections, with just one person in the front cabin where 20 were supposed to be sat.
The inquiry says this distribution would have shifted the centre-of-gravity to a position 38% of the mean chord, placing it "outside the flight envelope".
Although the cockpit-voice recorder did not provide relevant information about the accident, analysis of the flight-data recorder enabled Boeing to estimate a centre-of-gravity figure close to 40%, consistent with the calculation.
The twinjet received damage to the aft fuselage underside and tail-skid but none of the occupants was injured.
JIAAC has yet to reach conclusions on the circumstances of the accident but the carrier has revised procedures for controlling distribution of passengers and cargo on its aircraft.
The inquiry turned up a number of discrepancies in the aircraft preparation system. At the time of the event, Flybondi was using a company called FlySeg for dispatch at Iguazu Falls. The company operated from a structure similar to a shipping container located outside, about 200m from the check-in area, with a poor internet connection.
Although check-in is performed with a Radixx computer system, the company uses a separate and independent system called ARMS for 737-800 aircraft dispatch.
The airline's dispatch manual states that the ARMS system will be used to calculate flightplans and dispatch, but also has a procedure to carry out dispatch manually, indicating the forms necessary for determination of centre-of-gravity position.
JIAAC says the weight-and-balance envelopes in the ARMS system and those shown for manual dispatch – in the airport handling documentation – were different, with ARMS containing the correct version. The dispatch manual also lists methods of calculations for moments acting on an aircraft, using a Boeing 737-200 as a reference aircraft.