The phrase "downed hatch" refers to closing or securing a hatch on a vessel or aircraft. Synonyms for this phrase include "shut," "close," "seal," "lock," "secure," "fasten." Additionally, the phrase "downed hatch" can also be replaced with "sealed hatch," "locked hatch," or "secure hatch." These synonyms can be used interchangeably and depend on the context in which they are being used. In any case, the result remains the same, that the hatch is closed securely. A hatch cannot function properly if it is not downed, sealed, or locked; hence, it is essential to ensure that the hatch is always secure to avoid any mishap or hazard.