Fail to go in as they might go off? (1-5)

I believe the answer is:

a-bombs

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'they might go off?' is the definition.
The definition suggests an adverb but the answer is not.

'fail to go in as' is the wordplay.
'fail' becomes 'bomb' (synonyms).
'to go in' indicates putting letters inside.
'bomb' inserted into 'as' is 'A-BOMBS'.

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I've seen this clue in The Irish Times.

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