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Saturday, April 13, 2013

Lion Air 737-800 undershoots and ends up in the water

Lion Air flight LNI/JT904 flying from Bandung to Denpasar today ended up short of the runway and in the water this afternoon (13-Apr-13). The aircraft involved was PK-LKS, the aircraft is a Boeing 737-8GP with the possible serial number 38728, formerly used by Malindo Air for proving flights, the aircraft's first flight was 5 February 2013. The aircraft have only been in service with Lion Air Indonesia for less than since 28 March 2013 and appears to be a definite write off. The aircraft is also one of the few (if not the only) in Lion Air Indonesia's fleet that has a full In-Flight Entertainment on every seat by Panasonic.

PK-LKS ends up in the water short of the runway. Note the
perimeter fence is intact. (Source: Unknown via Twitter)
Contrary to initial media reports that stated the aircraft had overran the runway and ended up in sea, the aircraft never made it to the runway and instead of overshooting, it undershot the runway.

Weather at the time:
WADD 130730Z 15006KT 110V270 9999 FEW017CB SCT017 30/25 Q1007 NOSIG
(0730UTC/1530LT), Wind 150° at 6 knots varying from 110° to 270°, visibility more than 10 kilometers, few Cumulonimbus cloud at 1700ft, Temperature 30°C, Dew Point 25°C, Pressure 1007 milibars).

The Airport Ground Chart for Denpasar Bali (DPS). Note the geography for the western and eastern ends of the airport differ greatly.

Based on weather info at the time, and from ADS-B recordings of the flights preceeding and after the accident aircraft, the runway in use was runway 09. Overunning this runway would mean it should have crossed a major road and ended up in mangrove swamps and not in clear seas just off a runway!

Instrument Approach Chart for DPS 09
Based on ADS-B recordings, the following flights made their approaches for 09.

From 0550UTC:
- GIA439 KOEDPSCGK landed at runway 09.
- MAS851 KULDPS landed at runway 09.
- OZW251 PERDPS landed at runway 09.
- JST110 PERDPS landed at runway 09.

Following JST110 was LNI904. After LNI904 ended up in the water, VOZ4145 (SYDDPS) went around to 2000ft, and climbed to 3000ft and on hold at waypoint KUTA.
AWQ8497, held at 4000 at waypoint KUTA.
EVA255, held at 7000 at waypoint KUTA.
Possibly a CTV891 held at 5000 or 6000 at waypoint KUTA.
ADS-B recording of JT904 unfortunately was not enturely reliable, but it did show that VOZ4145 went around behind it.

Despite the past number of accidents and incidents at Lion Air, a significant safety improvements have been made over the past 5 years resulting in a huge drop in the number of mishaps per 10,000 departures for the airline.

Many are already asking if the accident was caused human error or mechanical or maintenance issues. While it is still early days, the following photo was sent to me reportedly from someone on duty at the airport at the time of the accident (the two aircraft was on hold), and if genuinely taken at around the time of the accident, can explain the weather information of the wind varying from 110° to 270° with that rain cell moving eastwards south of the runway centerline, carying with it some nice downdrafts (a.k.a. windshear).

Could this rain cell be responsible as one of the cuases of the accident?
Adding to the possibility of down drafts due to rain cells, approaching runway 09 also carry a risk of visual illusion. The lack of ILS (Instrument Landing System) and approach lights for the runway (the lack of the latter due to geography and ecological reasons), with only the PAPI (Precision Approach Path Indicator) as a cue of one's incoming slope on the visual part of the approach, raises the risk of losing depth perception, which in turn increases risk of undershooting the approach.

Whatever the causes, reasons, speculation, let the National Transportation Safety Committee investigate the accident. For me personally, I suspect the windshear and or the usual unstable approach as possible causes for this accident, but we must thank the low tide at the time of the accident as it certainly contributed to the high (100%) survivability rate of this accident.