Welcome to fire and forget ordnance, the moment missile/bomb leaves rail, you can’t do anything about its guidance.
ARH missile seeker runs with Pulse Doppler filter by default. Unless heli moves with considerable speed TOWARDS or AWAY from the missile seeker, it will be filtered out as ground clutter.
When heli flies high enough and IOG of the missile indicates very slow target speed, seeker will try to switch into Pulse mode. And if heli is high enough to distinguish itself from ground clutter, seeker will pick up and track heli. However, in this mode seeker is chaff vulnerable and heli can’t fly fast enough to trigger angle gating even if it tried to.
So yes, you can hit somewhat high flying helis… that forgot to equip chaff and/or are flying fast enough doing their best to headbutt missile that makes RWR scream.
Since Merkavas got IRST, you will have better chances of killing heli with IRST lock + time fuse HE than with any SPAA. Especially as IRST lock is/should be passive and don’t ring any alarms for the heli pilot except muzzle flash pointed at them.
Datalink is enabled by default for missiles that have it, all you can do is to pray. Pray target won’t notch your radar on purpose or by accident, nor gaijin servers decide to break datalink for any reason or no reason. Briefly losing TWS track also closes datalink channel. Then all datalink does is updates IOG, which in turn is ignored the moment seeker picks up anything. Which is usually “always” as ARH seekers go active around 16-20km from the target.
I mean, if I’m honest, it isn’t good, even with the random buffs they gave it, like being able to engage targets right in front of it, despite quite a few sources saying it has a min range of 2.5 or 3km? Or allowing its giant telephone pole missile to start turning right after launch, with dumb maneuverability compared to a Python 5. Any low-flying heli spanks that thing, and some jets can easily defeat it.
BUT TO SAY IT’S THE WORST AND WORSE THAN THE SPYDER IS INSANE
I imagine we will see Gaijin add the Arctic Pantsir with 18 missiles before we get a Spyder buff.