The operational maintenance mission – in which the sound barrier will be exceeded – of those fighter jets stationed at Air Base No. 5 (in Monte Real, in the municipality of Leiria) will take place, according to the FAP, near Figueira da Foz, between 4 pm and 5:30 pm.

“Although mitigating measures are being adopted to minimise impact, depending on atmospheric conditions, there may be a greater propagation of shock waves, making the phenomenon potentially audible and perceptible on the surface,” the Portuguese Air Force clarified in a statement.

The Portuguese Air Force (FAP) added that the effects may be audible in parishes in the municipalities of Leiria and Marinha Grande (Leiria district) and Figueira da Foz, Cantanhede and Mira (Coimbra district), reiterating that the operational mission “will be carried out under all safety criteria, without any risk to the population”.

To the Lusa news agency, an official source from the FAP clarified that it will be a flight involving “one or two F16M aircraft”, which should fly, as a rule, at a reference altitude between 30,000 and 40,000 feet (approximately between 9,000 and 12,000 metres).

“It is not expected to be below that. Nor should it be heard; if it is, it is a maintenance action on the aircraft, essential to their state of readiness. It is a safe, controlled flight; there is nothing alarming about it,” the same source reaffirmed.

At the end of April, another operational flight of F-16M fighter jets, where it was necessary to break the sound barrier, caused some alarm in the Figueira da Foz area, after a loud bang was heard and some effects resulting from the sound wave were felt, without, however, any material damage.

In the statement released, the Portuguese Air Force noted that missions such as the one planned for this afternoon are "essential to ensure the readiness and effectiveness of national air assets in safeguarding airspace, and rigorous control of the entire operation is permanently ensured."