From idea to take-off – preparing for a HALO measurement flight
No matter how many measurement flights we have already conducted, just before take-off the entire team assembles in front of the hangar and watches HALO's departure together. However, it takes days of planning and preparation to get to this point. For the SOUTHTRAC mission, all activities are carried out according to a fixed schedule, which is designed to ensure that flight preparations go as smoothly and efficiently as possible. Preparations for each flight take four days. As a measurement flight usually takes place every other day, several flights are always being planned at the same time, which is a complex task for everyone involved. At this point, I would like to present a timeline of the processes that have to take place before a measurement flight.##markend##
Four days before take-off
The planning of a measurement flight begins with a meteorological briefing for the scientists. Weather forecasts are compiled and evaluated, and possible objectives and flight routes are discussed. One challenge at this stage is that the forecasting models are still somewhat inaccurate at this timescale. It is therefore possible that the situation at flight time might differ from what is predicted at this early stage.
If the outlook for a flight appears promising, a flight plan is drawn up and submitted to our on-site flight planner, Andrea Hausold. She checks the feasibility of the plan and coordinates any necessary changes with the scientists. The flight plan is then submitted to the air traffic control organisations of all the countries over which HALO will fly. This defines the basic parameters of the flight for the first time.
Three days before take-off
The meteorological forecasts along the proposed flight route are now checked in daily meetings. Is the flight still feasible? Do changes need to be made to the waypoints or altitudes? This is the phase in which the most intensive discussions take place. From the scientists' point of view, it is always preferable to decide on the specific flight plan as late as possible, because the forecasts become more accurate. In contrast, the flight plan has to be submitted to air traffic control as early as possible, because they have to approve it. Meeting both sets of requirements is not always easy.
Two days before take-off
Two days before take-off, the time for discussion is over, as the final flight plan must be submitted. From this point on, significant changes to the flight plan are no longer possible. The DLR Flight Experiments team now draws up detailed schedules for the planned flight and begins organising the necessary logistics. This includes, for example, ordering fuel at the airport, and coordinating with the hangar staff and with the personnel responsible for the radiosonde ascents that will be conducted in parallel with the flight. In addition, the on-board crew are assembled and briefed.
One day before the flight
The weather is checked once again on the day before a measurement flight. On this occasion, the focus is more on the weather forecast on the ground. In Argentina it is currently quite cold and always very windy. If there has been frost overnight, precautionary measures need to be taken for some of the instruments, such as draining cooling water in order to protect the equipment from damage. If the crosswinds are too strong during the take-off or landing, these may have to be delayed slightly.
The initial preparations also get under way for the instruments. Individual components are serviced, and gas cylinders are exchanged or replaced. The GLORIA instrument, which was developed by Forschungszentrum Jülich and the Karlsruhe Institute of Technology (KIT), is already being continuously cooled with liquid nitrogen. Other instruments are calibrated for the upcoming flight.
Work begins on the day of the flight
This is when things get serious and the pace of work really increases. For many members of the SOUTHTRAC team, a daytime measurement flight means getting up early, as the initial tasks commence five hours before departure. The hangar is opened and the instruments in the aircraft are supplied with power from a Ground Power Unit (GPU). Shortly after, the final work on the instruments is discussed, and the concluding preparations begin.
Three hours before departure
One last meeting involving all of the groups of scientists takes place three hours before take-off. The status of all the instruments is checked one more time, and the experts take a last look at the route and the weather forecast. The meeting ends with what is known as a 'go/no-go decision'. This is the final determination as to whether the flight can proceed as planned, or whether it needs to be cancelled at the last minute.
One hour and 30 minutes before departure
As measurement flights are very long – at approximately 8.5 hours – and the flight crew needs to abide by strict working-hours regulations, those who are going to be on board arrive at the hangar only one-and-a-half hours before take-off. All of the crew members now go through the flight plan one last time and clarify any final details. This includes, for example, timings for certain flight segments, the climb and descent rates between points on the flight path, and the exact configuration of the turns when changing direction.
At this point, the whole team is busy working in the hangar – an average of 50 to 60 people. Space can get a bit tight in the aircraft.
One hour and 15 minutes before departure
The aircraft is now towed out of the hanger for the final pre-flight preparations. Doing this means briefly interrupting the supply of power to the instruments. This interruption needs to be kept as short as possible to ensure that the instruments can maintain a constant operating temperature. Taking the aircraft out of the hangar is therefore a highly coordinated undertaking. The power interruption is announced 10 minutes beforehand. Coupling the aircraft-towing tractor, shutting down the instruments, disconnecting the GPU, towing the aircraft out onto the apron, starting the Auxiliary Power Unit (APU) and powering up the instruments again must all be accomplished within three minutes. Achieving this requires the team to be well rehearsed.
One hour before departure
While the final preparations are being made for the instruments, a tanker drives up alongside the aircraft and commences fuelling. The pilots perform their checks and start up all of the aircraft systems.
Fifteen minutes before departure
All those who are not part of the mission crew must now leave the aircraft. Immediately after this, the engines are started, and the door of the aircraft is closed.
Five minutes before departure
The brakes are released, the pilots signal to the ground crew one last time and the aircraft taxis slowly to its take-off position at the end of the runway.
The engines are set to full throttle and HALO accelerates to its take-off speed. The crew depart on their measurement flight. The work is not over yet, of course. Over the coming hours, the flight will be followed closely both on the ground and in the hangar. Debriefing and data analysis will be carried out after the flight.
But it all begins with everyone standing in front of the hangar and watching the take-off together. Some take photographs, and almost everyone is smiling. It is always nice to see how everyone comes together and to witness the enthusiasm of the entire SOUTHTRAC team.