Airprox Serious incident ATR 72-600 (72-212A) PK-WHS, Tuesday 21 November 2017

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Date:	Tuesday 21 November 2017
Time:	01:31 UTC
Type:	ATR 72-600 (72-212A)
Owner/operator:	Wings Abadi Airlines
Registration:	PK-WHS
MSN:	1307
Year of manufacture:	2016
Engine model:	P&W Canada PW127
Fatalities:	Fatalities: 0 / Occupants: 66
Other fatalities:	0
Aircraft damage:	None
Category:	Serious incident
Location:	near Namp Island - Indonesia
Phase:	En route
Nature:	Passenger - Scheduled
Departure airport:	Sumbawa Besar-Brang Bidji Airport (SWQ/WADS)
Destination airport:	Lombok International Airport (LOP/WADL)
Investigating agency:	NTSC
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
Wings Air flight IW1861, an ATR 72-600 and a Cessna 172S (PK-BYK) were involved in an airprox incident near Namp Island, Indonesia.
The Cessna was being operated by Balai Pendidikan dan Pelatihan Penerbangan Banyuwangi (BP3B) on a cross country training flight from Blimbingsari Airport (WADY), Banyuwangi to Sultan Muhammad Kaharuddin airport (WADS), Sumbawa Besar.
PK-BYK with two student pilots on board departed from WADY with intention to cruise at altitude of 7,000 feet and
when approaching point KUBU TAMBAHAN, PK-BYK requested to Bali approach controller to climb to altitude of 9,000 feet which was approved.
At the same time, the an ATR 72-600 had departed from WADS with cruising altitude of 8,000 feet. The Pilot in Command (PIC) acted as PM and the Second in Command (SIC) acted as PF.
When PK-BYK was approaching point NAMP ISLAND, the Cessna's PF saw an ATR 72-600 aircraft flying through clouds from the opposite direction with the aircraft nose slightly up. The PF of PK-BYK assumed that the ATR 72-600 aircraft was climbing, so he decided to descend with the intention to avoid the ATR 72-600 aircraft.

The separation of both aircraft reduced to below minima when the PK-BYK pilot left 9000 feet at 01:31:40 UTC, the distance of both aircraft was 4.7 nm and continued reducing to a horizontal distance of 2 nm.
Both flights continued their flight to the destination safely.

Contributing Factors
The assumption of ATR72-600 on climbing and not aware of the right of way rules resulted in the PK-BYK pilot decided to descend aircraft for traffic avoidance.

Accident investigation: