Air Niugini Flight 73: Why the 737 Came Down in Chuuk Lagoon

Air Niugini Flight 73 was a Boeing 737-800, registration P2-PXE, flying from Pohnpei to Chuuk in the Federated States of Micronesia on 28 September 2018. On final approach, it flew into a tropical downpour, lost sight of the runway and kept descending until it struck the lagoon about 460 metres short of runway 04. Petter Hörnfeldt, a 737 captain who presents Mentor Pilot, walks through the official investigation and adds his own view, which he keeps separate from the report's findings.

An unforgiving airport

Chuuk has a single runway of about 1,830 metres with no runway end safety areas. Both ends run to the water. There is no control tower, and pilots announce their own positions on a common frequency. There is no ILS. Arrivals fly a GPS-based RNAV approach with a minimum descent altitude of 420 feet. Storm clouds build quickly in this part of the Pacific. On the day, the aircraft was lightly loaded, with 35 passengers and 12 crew.

An aircraft system nobody had been taught

P2-PXE was the only 737 in Air Niugini's fleet fitted with IAN, the integrated approach navigation system, which shows an ILS-style glide path on a GPS approach and lets the EGPWS give glideslope alerts. In 2015 the airline issued an order to remove it to standardise the fleet. The order expired before it was carried out, and the system was never written into the manuals or training. A maintenance engineer from the lessor, Loftleiðir, was riding in the jump seat and filmed the approach from about 3,000 feet. His video became key evidence.

The crew and the day before

The captain had 19,781 hours, including 2,276 on the 737. His route qualification for airports like Chuuk had been by observation only. His rest before the flight was 8 hours 50 minutes, short of the required 9 hours, although a medical specialist found no evidence that fatigue contributed. The first officer had 4,618 hours but only 368 on the 737. On the previous day's flight, the same crew had flown well below the glide path, and 28 glideslope alerts had sounded without either pilot responding. The report said that experience would have made the alerts seem like nuisance warnings.

The approach

The approach briefing was rushed, and the missed approach procedure was barely mentioned. The weather radar showed a storm cell between the aircraft and the airport. At 1,000 feet the approach was stable, and the first officer could see the runway. Selecting flaps 40 made the aircraft float slightly high. At about 677 feet the captain disconnected the autopilot to get back on profile. Two seconds later the aircraft entered heavy rain and the runway disappeared. The captain said, "Okay, landing."

Twenty-two seconds below minimums

The aircraft passed the 420-foot minimum descent altitude descending at about 1,490 feet per minute, with neither pilot seeing the runway. Over the next 22 seconds the EGPWS sounded seven glideslope and six sink rate alerts, and the instruments showed a pull-up warning. The captain answered the first sink rate alert with "I just want to get on profile." The first officer asked, "See the runway?" and then, about two seconds before impact, shouted that they were too low. The aircraft struck the water at 09:24 local time, skipped across the surface and turned through about 210 degrees.

Rescue

Chuuk had no water rescue service, but US Navy divers working nearby launched a boat within minutes, and local residents and fishermen came out in their own boats. Locals took 28 passengers and two cabin crew from the left overwing exits, and the divers took six passengers, four cabin crew and a loadmaster from the other side. The pilots and the engineer left through the forward door. One passenger, in seat 23A beside the fracture, died of head injuries. Other passengers said he had been standing during the approach. Six passengers were seriously injured.

What the investigation found

The investigation found the captain had become fixated on landing, filtering out the warnings, and the first officer had been working from an out-of-date picture of the approach. It recommended a harder aural "pull up" warning. The NTSB, representing the state of manufacture, disagreed. It noted that the crew had disregarded 16 alerts in the final 19 seconds. Air Niugini added sudden loss of visual reference to its simulator training. Hörnfeldt's closing advice is the oldest rule in flying: when an approach stops being stable, go around.