Fears over a cancer causing substance in the cockpit of the F-16I has led Israel to stop training flights of their fleet of 62 aircraft. It was
recently discovered that formaldahyde was leaking into the cockpit, possibly from the air conditioning system. Lockheed is investigating reports
recently about the air quality of the birds. All 125 F-16C/Ds are fully operational and haven't reported any problems.

Fears about a cancer-causing substance in the cockpit has prompted the Israeli Air Force (IAF) to suspend training flights for its 62-aircraft
fleet of Lockheed Martin F-16I Sufas.
“According to tests the substance is formaldehyde that recently was defined as causing cancer above certain concentration,” says the IAF
spokesman
Source