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6 July: Washington-New York City

“Adventure with a capital A is always made of great satisfaction but also difficult times. And if each flight of our 2013 crossing "Across America" in this respect can claim the stamp "Adventure from inside", I think that this ultimate flight of HB-SIA represents something exceptional.


Lead shot in the solar bird's wing

It is 9.15 pm in Payerne, and the tension is visible on everyone's face. For the first time since 2010, when the HB-SIA made its first flight, we are all aware that the plane could be forced to make an emergency landing.

Ray, our flight director, just tells us the news. A portion of the fabric covering the underside of the left wing is torn, revealing a quite wide opening under this wing. It happened a little before our waypoint "PANZEE" above the Atlantic Ocean, a place where we are supposed to have a long 5-hour holding.

The situation is described in less than 30 seconds and we discuss the possible consequences with Ray. Then we all go back working to examine the conditions for an emergency landing: where, when, how long to reach every possible airfield, how to manage energy in batteries, how is the wind and what is the risk of turbulence during the descent, what is the surface wind on each possible runway... Meanwhile, the U.S. air traffic is warned of our difficulty, as well as the coast guards.

MCC: mission "crisis" centre

At the mission control centre (MCC), we are prepared for this type of situation. During the multiple virtual flights we have performed since 2007, we have been trained for situations of “crisis”, deeply changing the flight plan and forcing us to define a new flight strategy within a short time.

These trainings have allowed us not only to know what we have to do, but also what others have to do. In such conditions, success is due to the team spirit in which we work. But tonight, the atmosphere has suddenly become strange, because what could happen has just turned into reality.

On the simulation team side, we must work fast. We calculate the different possibilities to reach without delay the selected airports. The conditions are far from ideal as it is only 3.30 pm in the aircraft, which means that, due to thermals, we will potentially find turbulent situation as soon as we return above the mainland. Alternative strategies are studied and transferred to Ray who discusses with Andrew. On the screen, his face also shows an intense concentration. He is 6,000 kilometres far from our MCC, but we have probably never felt him so close to us.



A decisive decision

Then the decision is made to try to rally New York, flying along the coast, in order to avoid thermal turbulences which could further damage the plane. Nik, Michel and Yves-André have just negotiated with the U.S. air traffic control the authorisation for André to leave immediately his holding and fly directly to JFK Airport.

Luc and Wim refine wind forecasts for early arrival at JFK, and determine the characteristics of the Low Level Jet we will encounter, a little before midnight, above the "Lower New York Bay".

We know that the next hour will be decisive. If the situation remains stable, then we should actually be able to join New York. And while continuously scrolls across the screen the pop-up message explaining that due to a technical problem, the HB-SIA will land earlier at New York, I think at this point, we all remember the last 48 hours of preparation: the weather situation which improves gradually until it becomes almost ideal for a take-off this morning, the numerous calculations to optimise the strategy of low-altitude flight, completely new, the flight plan which becomes a reality once accepted by the U.S. air traffic control, the final GO and take-off this morning exactly on time, and the plane which rushes forward on the Washington runway and leaves the ground with always the same incredible ease...

Ready for landing

The helicopter monitoring the evolution of the situation tells us that the tear has stabilised. This is of course very good news. And while André keeps on flying to New York, our work focuses on the details of his arrival, and in particular the choice of the runway to request to the control tower.

This choice is made depending on the wind direction for landing, but the low level jet complicates our task because it does not have the same orientation as the surface wind. Ultimately, the 31L runway is the best solution, even if the approach is less direct than in the case of the 22L runway, easier to reach from Jamaica Bay. The U.S. air traffic control asks us a precise timing to overfly the last waypoints and for the final approach, so we recalculate again all crossing points to provide the requested information.

In New York, everyone is also preparing for landing. The images show Tahan who monitors the wind speed and the presence of ground gusts, anemometer in hand. André is now 30 minutes from the airport, in flight over the Lower New York Bay at 3,000 feet. We follow the progress of the flight on our screens, we monitor the crossing times to waypoints and wind speeds displayed on the telemetry screens. André begins its descent just before entering Jamaica Bay. Slowly, the altimeter displays the figures marching irresistibly ahead. At 1,500 feet, in the Low Level Jet, the wind is still 20 knots, it is much but is expected to weaken lower, around 500 feet or maybe even below.

Finally, the screens show the aircraft overflying the runway. At 300 feet the wind calms down a bit, but if the aircraft remains stable, telemetry shows how André is actually highly maneuvering the stick at all times to maintain stability. His work is impressive. Thirty metres, twenty metres, ten metres ... seconds seem long and an extraordinary silence has fallen over the MCC. Finally, the landing gear touches the ground and the aircraft is still running a few seconds on the runway before stopping.


Mission "Across America" accomplished!

And suddenly, whereas with this very last and ultimate step of the “American adventure” also end HB-SIA flights, now retired, I think I came back to remind the memories of ten years ago, at the beginning of this incredible project...

My very first meeting with André, in his office at the EPFL, when he grabbed a A4 paper sheet to draw the principle of solar-powered aircraft... The lunch we had together, and which gave me enough time to analyse the complexity of such a project…

My explanations on the blackboard in the afternoon, so as to present André the modelling methodology that I was recommending to faithfully represent and optimise such a plane. And finally, my feeling on the way back to Paris, that this would certainly be the most extraordinary project I would have to work on, in my life as a mathematician."



Christophe Béesau

Altran expert on Solar Impulse for Advanced Modelling and Simulation