High levels of Formaldehyde have been found in the cockpits’ of F-16I’ss.

The F-16 I (see picture below), is a variant unique to the IAF, with conformal tanks and a spine for additional avionics, and given the IAF’s specific needs, it likely has an air conditioning system tailored to this equipment, which is likely the source of the contamination.

It could come from combustion, but the path from combustor to cockpit would be unlikely.