Here’s your hand sitting south and the auction:
♦ 9♣ AK
South West North East
2D* P 2H P
*Transfer to hearts
You’ve got 3 quick tricks, 14 HCP, 8 hearts, and only 4 losers, a hand with which you could open a strong 2C, and your partner opens 1N! How do you search for slam? All you want to know is if your partner has the Ace or King of Hearts. If you jump to Blackwood, that won’t do you any good. Regardless of whether or not you are playing standard or Roman Key Card or 1430, partner’s response showing only one ace or key card leaves you in the dark. You only need to know if she has the ace or King of hearts. You just have to trust and assume that her bid includes the Ace of diamonds.
So Blackwood is an imperfect response. So are bids of 3 Hearts, which would only be invitational and may be passed, or 4 hearts, which is a closeout unless you play Texas Transfers. And even if you play Texas Transfers (1N-4D is a transfer to 4 hearts, etc.), there’s no way partner can visualize your hand with its 8 card heart suit.
(To digress, people who pay Texas Transfers often use the bid of 1N-2D-2H-4H as showing a stronger hand than 1N-4D-4H.)
But there is a bid I use in such situations. South would bid 5H after partner accepts the transfer by bidding 2H! What does that mean? Some experts play a jump like this to five of a major as a “Grand Slam Force” with special meanings to all the responses, but that’s too complex for what I'm suggesting here. The way I use it with my partners is that a jump to 5 of the agreed major suit (which bypasses game and blackwood) in this situation asks partner, “How good are your trumps? Because partner promises at least 2 hearts with her opening bid of 1N, if she has two small hearts, she passes. While the question is ambiguous (how “good” is good?), one needs to use common sense in responding. If, however, my partner made this bid and I had the Ace or the King, I would bid 6 hearts.
This hand came up in a three table Swiss Teams game and neither table got to the slam because nobody knew this bid. Here are the four hands:
♠ JT953 ♠ 76
♥ A6 ♥ 8
♦ K842 ♦ 653
♣ J8 ♣ 976432
Since North had K9 in hearts (along with the spade King and diamond ace, which were no surprise with her 1N open), she should bid 6, which was cold. This is a bid that you should discuss with your partners and add to your repertoire.