After update to 10.3.3. (via ota) there's no modem firmware and always searching (imei is OK), then restart after some minute.
I've restored (via itunes) with same 10.3.3, then everything is OK, but after 2 days, when i insert sim (ipad in airplane mode) the same things happened :
searching & no modem firmware.
It was working well for 5 years, now my ipad is useless.