The Heli Pilot will periodically produce bursts of wind that are capable of blowing back up to 1 bloon every 0.15s (every 0.12s with 0-3-2), equivalent to around ~6.67 bloons per second (every ~8.33 with 0-3-2). Considering its consistent blowback power, it is best used against strong non-MOAB-class bloons like Ceramic Bloons (especially against Super Ceramics).
Downdraft is the most reliable option for blowback in the game, due to its effective manual control and consistent blowback. While expensive compared to other blowback options, its high controllability makes it an ideal option on any map condition, including the hardest of maps. It sees the most use in late-game runs when used to reduce progress of Super Ceramics from particular areas along the track, particularly in CHIMPS Mode. In addition to simply blowing back progress of Super Ceramics anywhere, Downdraft is a popular and reliable choice for stalling, often paired with 0-1-2 Ice Monkeys for near-infinite stalling.
There is no major advantage of using crosspathing, so using 0-3-0 is generally sufficient for applying consistent blowback against bloons. Crosspathing can be added to assist with necessary applications, whether it be needing automatic targeting via Pursuit or blowing back bloons at a faster rate.
Try the Pursuit upgrade for relatively easy blowback against the Ceramics that spawn from MOABs.
Alternatively, if manual micromanagement is preferred, use the 0-3-2 Downdraft (with Faster Firing) for a faster blowback rate.
Pair this with 0-1-2 Ice Monkeys for good stalling of Super Ceramics.
Technically speaking, the Downdraft effect can be improved via Berserker Brew and Stronger Stimulant, which will allow it to blow back a greater number of bloons at a faster rate because of the combined pierce and attack speed buffs. However, the Downdraft effect will consume Alch buffs quite quickly whether or not its other attacks are active or not, which means increasing blowback power by those methods aren't always reliable.
There is an interesting interaction with Frozen Bloons whereby the Downdraft effect can affect them only after the bloons defrost. This was discovered in Version 25.0 after Ninja Kiwi applied a damage types rework for many towers in the game.
Downdraft is especially useful at holding back Super Ceramics nearing the exit and providing an option to stall rounds once all blimps are popped.
Because of how cost-efficient and effective its blowback power is compared to other options, Downdraft's blowback rate was nerfed for the non-crosspathed variant to reduce the power of 2-3-0 Downdraft. On the other side, 0-3-2 Downdraft's blowback was buffed overall to reward players for proper Downdraft micromanagement.
Pursuit Downdraft has felt like an overperformer for a very long time, but instead of outright nerfing it we increased crosspath potential for those who manually take control over their heli micro. [...]
~ Ninja Kiwi
030 blow rate reduced from 0.125 → 0.15
032 blow rate increased from 0.125 → 0.12
Crosspathing in BTD6 (top path 1, bottom path 3)
Downdraft with the blowback animation on BTD6
Official BTD6 upgrade artwork
Official BTD6 upgrade icon
Instamonkey icon for Downdraft
In BTD6, this upgrade costs $500 more than in BTD5 for the upgrade alone ($3000 instead of $2500), but overall a 0-3-0 costs $400 more than the respective BTD5 crosspath counterpart due to the Bigger Jets cost decrease and base Heli Pilot cost increase.
There was a strange interaction with Downdraft and Monkey Intelligence Bureau whereby MIB allows Downdraft to blowback Leads but not Frozen, even though Downdraft normally blowbacks neither Frozen nor Lead. As of 25.1 testing, this glitch no longer exists. Instead, Downdraft is unable to blowback Lead or Frozen Bloons completely. Frozen Bloons unfrozen are still are blown backwards if affected by at least one Downdraft effect, even after 25.1.