Navy flyovers

I'm watching the final coverage of President Bush's burial ceremonies in Texas.
There was a 21 plane flyover, all planes had their tail hooks lowered.
I live near Arlington Cemetery, and I've noticed this on several occasions.
Does anyone know what the significance of this might be ?

Its the missing man formation flyover. Normally not 21 aircraft. Its a way for aviators to may respect for lost aviators. OBTW this is one of the largest. Not sure if significance of 21 aircraft is tied to 21 man gun solute or not.

InProcess said:

Its the missing man formation flyover. Normally not 21 aircraft. Its a way for aviators to may respect for lost aviators. OBTW this is one of the largest. Not sure if significance of 21 aircraft is tied to 21 man gun solute or not.

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I think he's asking about the tailhook down.
Missing man is simply when one airplane soars up out of formation as they pass over, or they can just fly over with that slot empty. I don't really understand why they had all those groups of planes fly over, but only one missing man group.
And I can't remember the significance of the number "21." Something about showing peaceful intentions.

Ive been told that hook down is just another way to show respect.

Not sure, but I believe it signifies the final “trap” (carrier landing).