Airbus brake-to-vacate technology has wide-ranging applications
A380 developments include runway performance tool that can improve business aviation safety.
After selection of BTV exit, performance margins are shown on the airport diagram for "Dry" and "Wet."
We set up a flightplan that would bring us to the south of the airport to FL100. From there we would return to TLS to do a number of approaches, go-arounds and landings to demonstrate the functions of the BTV system.
After pushback and engine start, we taxied out to the runway, and it was obvious that the A380 still draws a crowd, as quite a number of spectators and spotters lined the airport fence to see this very large aircraft fly.
Our ZFW was 300 metric tons and we carried 84 tons of fuel. Our takeoff weight of 384 tons (844,800 lbs) was still way below MTOW, which can be over 500 tons, depending on the version.
After Lelaie handed me the controls, I advanced the throttles and with a smooth pull on the sidestick I lifted F-WWOW up into the skies of southern France.
We turned south and climbed toward the French Pyrenees —the snow-covered mountain range that defines the border with Spain. While cruising at FL100 over this gorgeous panorama, we set up the FMS for the approach to TLS.
Setting up the BTV system
When returning to larger ranges for inflight descent navigation, selected runway and exit remain visible, but not taxiway diagram.
On Airbus aircraft, the airport weather (wind, pressure, temperature) is always typed into the FMS before landing. In addition, for the BTV system to work, it is necessary to zoom in on the navigation display (ND) to call up the taxi chart.
With the help of the CCD, the cursor is placed over the runway designator and the runway thus selected.
At this point 2 markings appear on the runway symbol—"Dry" and "Wet"—which depict the points on the runway where 10 kts GS will realistically be reached after landing. Calculation of these points differs from certified performance calculations and from actual performance.
Airbus uses values that it calls "required realistic operational landing distance" and has these values stored in a database.
In a 2nd step, a taxiway is selected. For a smooth rollout, it is desirable to select a taxiway beyond the Wet mark—but any taxiway up to the Dry mark may be used. Now the autobrake selector is placed in the BTV position (not LO, 2, 3 or HI) and the system calculates the deceleration rate required.
As an added bonus, the expected ROT in seconds and the time to cool the brakes in a minimum turn-around (MTT) are displayed. At 4000 ft, 12 nm from the airport, the controller turned us onto final approach to Runway 32L—a runway which is long enough for flight test and is primarily used by Airbus. Rwy 32R is used for commercial and executive traffic.
I turned off the autopilot and autothrottle and flew the A380 manually on the ILS. Our landing weight was now 350 tons. We had also spent some time trying other new avionics systems at cruise level which will be the subject of a future story.
An A380 for Air France lands at TLS during predelivery flight testing.
Down to 500 ft, BTV performance values are based on numbers stored in the BTV database. Below 500 ft, actual and expected performance are compared continously. For the first landing we selected Taxiway S10, which is all the way down the runway.
After touchdown I opened reversers 2 and 3, the A380 slowed down at a majestic pace. Only when we reached 45 kts did the autobrake system come in, and it did so smoothly. This is obviously the most "caressing" way in which to slow down an aircraft and not always an operational possibility.
We taxied back and took off for a number of patterns to try out different landing scenarios and the resulting behavior of the BTV system.
If an exit is selected which only allows a landing on a dry runway, the warning, "If wet, runway too short" appears on the PFD. The last 2 approaches were the most impressive. BTV always compares the actual with the calculated deceleration rates. If deceleration is not sufficient, the system generates an ROW.
If the approach is too fast and not stabilized, then at 500 ft the warning "Rwy too short" appears in the PFD, combined with a synthetic voice callout to go around. The final decision to go around still rests with the crew.
Warnings and protections
In order to generate the warning on an otherwise perfectly safe runway, we had shortened the runway in the FMS by 1800 meters at the runway end. We also deliberately flew 25 kts above the correct approach speed.
So we were acting as 2 bad pilots, flying too fast and trying to land on a runway that was much too short. Just as expected, the system asked us to go around in very clear terms at 500 ft.
I pushed the TOGA button and we pulled up. A go-around in a A380 is always an impressive maneuver—hundreds of tons of technology were pushed back up into the sky by the 4 Rolls-Royce Trent 900 engines.
Now we returned to our final landing, this time with the intention of ignoring the ROW and landing despite the warning. As mentioned, we had shortened the runway, but only in the FMS—the real concrete being comfortably long enough. After all, the flight test environment is a very controlled and professional one. Nothing is left to chance.