Significant updates mean 777X faces rigorous assessment en route to certification

[Ref Flight International Magazine 11-17 Feb 2020]

Experts doubt the 737 Max crisis will significantly impact 777X certification, although it may lead regulators to look more closely at safety analyses and pilot response assumptions.

Boeing intends to certificate the 777X as a 777 variant, not an entirely new aircraft.

But various changes could be found in the 777X, include a 2.9m (9ft 6in) stretch to the fuselage over the 777-300ER, a longer composite wing with folding tips, and new GE Aviation GE9X engines.

The 777X must undergo a thorough shakedown because of significant updates Boeing has made, says Peter Lemme, an ­aerospace consultant and former Boeing engineer.

Meanwhile, some experts expect flight testing will take about one year – a fairly standard duration.

Using the Airbus A350-900 flight-test campaign as an example, it lasted 15 months and used five aircraft flying some 2,600h.

The first few weeks typically involve proving the aircraft flies as expected. Flight-test programmes will then move to validating engineering models and assumptions related to aerodynamics, engine performance and fuel flow. After that, it comes tests involving system failures and performance at hot and cold temperatures and with tailwinds and headwinds.

This time, the Boeing tends to use 4 aircrafts in the test fleet. WH001, will test avionics and related system, brakes, flutter, icing, stability, control and low-speed aerodynamics; WH002 will trial auto-land, ground effects, stability and control; WH003 will be used to evaluate the auxiliary power unit, avionics, flight loads and propulsion performance; WH004 will test the environmental control system, extended twin-engine operations, noise and general functionality and reliability.

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