Enhanced FBI, a great new flight test capability and it's price

Chris Worning, Experimental Test Pilot, Airbus Defence & Space, Germany

Abstract

A very powerful new flight test tool was developed for the Eurofighter flight control system. In the past the Autopilot was re-programmed for flutter excitation, the so-called Frequency Biased Inputs (FBI), and later simple control inputs were added to be able to fly perfect rudder doublets. In the continuous pursuit of still better flight test data, but also for quicker clearances, a whole new set of manoeuvres were programmed, it was called enhanced FBI.

One may think that this automation would insult the professional pride of test pilots, but in fairness, to stabilise the test conditions for the required time in all corners of the envelope was more than enough of a challenge in itself, and the data provided by the eFBI was better than any human could provide.

But as so often this wonderful new capability came with a price. The magnitude of possible test cases and the associated clearance limitations turned out to be a Pandora's box of potential errors, that could result in massive limit exceedances with potentially disastrous results, so the risk mitigation became complicated.

The purpose of this paper is to describe the potential pitfalls created by this new flight test capability, and the measures taken to avoid them. It is my hope to provide food for thought for other flight test organisations faced with complicated test tasks and/or clearance issues.