As a general rule, the position of the ball in relation to the goal line is always reviewable by instant replay.
Limitations on Reviewable Plays
ARTICLE 7.No other plays or officiating decisions are reviewable. However, the replay official may correct obvious errors that may have a significant impact on the outcome of the game, including those involving the game clock, whether or not a play is reviewable. This excludes fouls that are not specifically reviewable (See Article 8, following).