The crash is the latest in a string of deadly accidents involving surplus and often old foreign aircraft acquired by the Philippine military.
The air force's fleet of 30 Broncos were acquired from the United States in 1991 and Thailand in 2004.
Developed in the 1960s as a counter-insurgency aircraft by the US Air Force, the Broncos can carry heavy ammunition for a few hours in the air.
They are used primarily for close air support missions against Muslim and communist insurgents, mainly on the southern island of Mindanao, Okol said.
However, they are also used to monitor the archipelago's extensive coastal areas, as well as for search and rescue missions in the disaster-prone Philippines, he added.
Okol would not say exactly how old the crashed plane was, but insisted that all of the Broncos were in good condition.
"They have received a good number of upgrades, and we maintain them very well," he said.
The Philippine military is among the most poorly equipped in the region, and past modernisation efforts have consisted mostly of surplus hardware acquired from its traditional ally, the United States.
In May, two pilots were killed when an air force trainer plane crashed north of Manila
In 2010, eight air force personnel and a civilian were killed when a light cargo airplane crashed in the southern city of Cotabato.
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