A330 flight crew reported a TCAS RA and near midair collision with a PA42 on the HYPER7 STAR to iad.

Attributes
ACN	1486541
Time
Date	201710
Local Time Of Day	1801-2400
Place
Locale Reference	IAD.Airport
State Reference	DC
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	A330
Operating Under FAR Part	Part 129
Flight Phase	Initial Approach
Route In Use	STAR HYPER7
Flight Plan	IFR
Aircraft 2
Make Model Name	PA-42 Cheyenne IIA
Operating Under FAR Part	Part 91
Flight Phase	Climb
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Person 2
Function	Other / Unknown
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Conflict NMAC Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance
Miss Distance	Vertical 100

Narrative:

At around 4500 ft descending on the HYPER7 STAR to 19L waypoint yyang passed inbound dadey; cleared to descend according the STAR; cleared to intercept the localizer 19L; we received a TCAS TA. Even coming directly out of the sun the intruder was quickly identified about 300 ft lower approaching fast from a 1 to 2 a clock position directly towards us. The PF reacted instantly and followed the upcoming TCAS RA. Even with this quick reaction the intruder; a PA42 twin turboprop; passed just 100 feet (-01red) below our cockpit. ATC was very busy and our TCAS RA call could only be sent with some delay. Our information; TCAS RA; nearmiss; twin turboprop 100ft lower; was not commented by ATC but we were cleared to descend to 3000 feet for the ILS 19L. We landed without further disturbances.

Original NASA ASRS Text

Title: A330 flight crew reported a TCAS RA and NMAC with a PA42 on the HYPER7 STAR to IAD.

Narrative: At around 4500 ft descending on the HYPER7 STAR to 19L waypoint YYANG passed inbound DADEY; cleared to descend according the STAR; cleared to intercept the LOC 19L; we received a TCAS TA. Even coming directly out of the sun the intruder was quickly identified about 300 ft lower approaching fast from a 1 to 2 a clock position directly towards us. The PF reacted instantly and followed the upcoming TCAS RA. Even with this quick reaction the intruder; a PA42 twin turboprop; passed just 100 feet (-01red) below our cockpit. ATC was very busy and our TCAS RA call could only be sent with some delay. Our information; TCAS RA; nearmiss; twin turboprop 100ft lower; was not commented by ATC but we were cleared to descend to 3000 feet for the ILS 19L. We landed without further disturbances.

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.