Guyanese investigators have disclosed that a Fly Jamaica Boeing 757-200 suffered significant hydraulic failure as it returned to Georgetown’s Cheddi Jagan airport, with the subsequent loss of braking effectiveness causing the twinjet to overrun and sustain severe damage.

All 120 passengers and eight crew members survived the initial accident and evacuation, although one elderly passenger died five days later.

Some 10min after taking off from Cheddi Jagan on 9 November 2018, bound for Toronto, the aircraft had reached 20,000ft when the crew informed air traffic control that they were returning to the airport, citing a hydraulic problem.

The left-hand hydraulic system had low fluid quantity, says the Guyana Aircraft Accident & Incident Investigation Unit, which published its final report in late May.

It states that the power-transfer unit activated automatically, to enable the right-hand hydraulic system to pressurise the left. This was not possible, owing to the fluid loss, but the power-transfer unit did not shut off – the result of a latent failure of its control-circuit pressure switch.

The power-transfer unit consequently ran in a no-load condition, causing the right-hand hydraulic fluid temperature to increase.

Fly Jamaica 757 accident

Source: Cheddi Jagan airport

Loss of hydraulic pressure left the crew without access to normal braking

As the aircraft conducted its approach to runway 06, it was configured with 20° flap and its landing-gear was deployed with the alternate extension system.

But while the right-hand engine-driven pump could maintain the hydraulic pressure during this phase of flight – even with the power-transfer unit’s no-load condition – the retardation of thrust during the flare made this demand unsustainable.

The right-hand hydraulic pressure dropped to zero – unbeknown to the crew – leaving the pilots without normal braking function, and only accumulator braking available.

Quick-reference procedures for loss of pressure in both left and right hydraulic systems advise that, with accumulator braking, the crew should apply steady, increasing brake pressure to decelerate and stop.

But the inquiry says the crew, believing the right-hand hydraulic system was functioning, “pumped” the brakes several times which “depleted” the accumulator pressure.

With the flaps at just 20°, the aircraft had landed at a high speed of around 160kt, exacerbating the difficulty of slowing and stopping, particularly with the spoilers and thrust-reversers affected by the hydraulic failure.

Flight-data recorder information shows the aircraft veered to the right as it decelerated before exiting the runway and coming to a halt as its right-hand main landing-gear became embedded in soft ground. The jet’s right wing was damaged by ground contact, with its Rolls-Royce RB211 engine almost separating, and the nose-wheel was some 30ft short of a steep drop-off.

The inquiry says the “totally unexpected” failure of the right-hand hydraulic system almost at the point of touchdown “would have taken the [pilots] by surprise”, with its suddenness potentially affecting their ability to react.

“It is believed that the [crew’s mindset] for maximum manual braking may have contributed to loss of situational awareness after the aircraft touched down,” it adds.

Investigators have attributed the loss of hydraulic pressure in the left-hand system to inadequate maintenance, pointing out that flight-data recorder information had indicated a “trend” of hydraulic difficulties particularly during the six flights prior to the accident.

Boeing had noted, in a February 2001 service bulletin, six occurrences of dual hydraulic system loss on 757s. Each involving depletion of left-hand hydraulic fluid through a ruptured main-gear downlock hose, followed by right-hand system overheat owing to power-transfer unit switch failure.