C402 captain reported his aircraft was rolled into a 90-degree bank from wake turbulence at 300 feet...

Narrative:

Coming in on the visual 4L; I was 4 miles behind a heavy airbus A340 on final for 4R. At 300 feet the airplane rocked and bounced wildly; and the airplane went into a right roll. I was able to recover the roll at what I can only estimate to be about 90 degrees. People were bounced out of their seats; and pinned against the right side of the airplane. I struggled to control the airplane; applying full left aileron and rudder to attempt to correct the roll. Finally I was able to straighten the aircraft. I executed a go around at full power. We came back into land on 4L without incident. I asked the passengers once in the air when we got leveled out; and twice on the ground if anyone needed any assistance. The only passenger that spoke up was a female who had previously had back surgery. She stated her back hurt and that she would need to take her pain medicine now. She also asked for a wheelchair which I already had plane-side for her. Wake turbulence from the heavy airbus; plus a 15 knot crosswind; blew the wake right into my aircraft; thus causing it to become uncontrollable.

Original NASA ASRS Text

Title: C402 Captain reported his aircraft was rolled into a 90-degree bank from wake turbulence at 300 feet AGL on approach into BOS 4 miles in trail of an A340.

Narrative: Coming in on the visual 4L; I was 4 miles behind a heavy Airbus A340 on final for 4R. At 300 feet the airplane rocked and bounced wildly; and the airplane went into a right roll. I was able to recover the roll at what I can only estimate to be about 90 degrees. People were bounced out of their seats; and pinned against the right side of the airplane. I struggled to control the airplane; applying full left aileron and rudder to attempt to correct the roll. Finally I was able to straighten the aircraft. I executed a go around at full power. We came back into land on 4L without incident. I asked the passengers once in the air when we got leveled out; and twice on the ground if anyone needed any assistance. The only passenger that spoke up was a female who had previously had back surgery. She stated her back hurt and that she would need to take her pain medicine now. She also asked for a wheelchair which I already had plane-side for her. Wake turbulence from the heavy Airbus; plus a 15 knot crosswind; blew the wake right into my aircraft; thus causing it to become uncontrollable.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1675526
Time
Date	201908
Local Time Of Day	1201-1800
Place
Locale Reference	BOS.Airport
State Reference	MA
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Cessna 402/402C/B379 Businessliner/Utiliner
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	A340
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	ATC Issue All Types Inflight Event / Encounter Loss Of Aircraft Control Inflight Event / Encounter Wake Vortex Encounter

C402 captain reported his aircraft was rolled into a 90-degree bank from wake turbulence at 300 feet AGL on approach into bos 4 miles in trail of an A340.