Leading 1-0 after Edeh Chidi's 60th minute strike, the last year's runners up got the shocker in the 90 + 1st minute when Henry outran East Bengal defender Uga Okpara before firing past goalkeeper Gurpreet Singh.
East Bengal dropped to 41 points, two points behind leaders Churchill Brothers, who have played a match less than the former.
Credit should also be given to Air India's Sukhwinder Singh who stood tall under the bar, thwarting four chances.
Chidi had a fine shot outside the box in the 22nd minute, but Sukhwinder saved it.
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East Bengal finally tasted success when Chidi well trapped an Andrew Barisic low cross before scoring a left-footer.
With Sukhwinder doing a fine job, Air India did not let in any further goal and when it seemed that East Bengal were pocketing a full three points Henry produced a beauty in the dying minutes.
It was too late for East Bengal to bounce back as the draw meant a big setback for their I-League title hopes.