One aspect of the Greenhouse gAs Uk and Global Emissions (GAUGE) project is to use aircraft measurements to help determine UK emissions from a variety of sources, thereby helping to quantify the UK’s greenhouse gas budget. Dr Grant Allen, from the University of Manchester manages this aspect of the project, and spoke very eloquently about the role of aircraft measurements in a recent episode of the Barometer Podcast: GAUGE - From the Air.

The FAAM BAe-146 in flight (Source: FAAM).

Primarily GAUGE will be using the UK’s BAe-146 large Atmospheric Research Aircraft (ARA) to help constrain emission estimates across the whole of the UK. The first phase of this flying programme will take place in April (with further flights planned for July and August) 2014, and we are now at the stage where detailed flight plans need to be produced, so that they can be discussed by the pilots and scientists, and then iterated accordingly. But what exactly is a flight plan, and why are they needed in the first instance?

The flight plans that are used by the Facility for Airborne Atmospheric Measurements (FAAM), the institution that helps to run the ARA, are known as Sortie Briefs; examples of which can be found by clicking on any of the previous flights (labelled Bxxx) in the FAAM flying programme calendar. These Sortie Briefs are the final document that is given to the crew of the ARA in the mission briefing prior to take-off, but they typically undergo several revisions beforehand.

The first step in developing a Sortie Brief is to determine the science objectives for the flight; this is done by asking the scientists involved what their ideal scenario would be in terms of measurements; for example, one of the planned flights for the GAUGE campaign is for a lap around the UK to try and quantify emissions at this nationwide scale. Once this wish list has been discussed, the next step is to see if such a flight is feasible. The ARA has a maximum flying time of about 5 hours, with a typical flying altitude of 200 nautical miles per hour (~ 230 mph, 370 km/h), and so any flight that exceeds these limitations will need to be modified accordingly; in the case of a lap around the UK, any flight plan would therefore need to include a refuel (e.g. in Aberdeen). Google Earth is a great tool for calculating these initial distances and for determining the viability of a flight.

A potential flight plan for another GAUGE flight, this time for a triangle centred on the Northern cities of Liverpool, Leeds, and Manchester City, AKA the Robbie Fowler triangle (so called because the footballer Robbie Fowler has turned out for a team in each of these cities) (Source: Google Earth, 10th Oct 2013 and 8th Feb 2014).

Once the scientists are happy that the planned route meets their objectives, and the feasibility of the flight has been assessed, the mission scientist(s), i.e. the scientist(s) coordinating the flight, will communicate with Directflight (the Airtask group that provides bespoke mission based aviation solutions to FAAM) as to what is really possible with the flight. Owing to existing flight corridors, airports, and military no-fly zones, there are certain areas that are simply not possible to fly through, and so it is not until after this consultation that the flight path can be truly determined. Thankfully experienced mission scientists have an in-depth knowledge of many of these no-fly zones, which can help to expedite this process. However, Notices to Airmen or NOTAMS can really throw a spanner in the works. NOTAMs are notices filed with an aviation authority to alert aircraft pilots of potential hazards along a flight route, or at a location that could affect the safety of the flight, and they can be posted anytime up to 24-hours before a potential flight, causing further headaches for the flight planning team.

Map showing the NOTAMS navigation warnings for Tuesday 18th Feb 2014 (Source: NOTAMS).

Another thing to consider when planning a mission, and a crucial element of any Sortie Brief, is the weather. The mission scientists will check long-range forecasts for up to two weeks before a planned flight to see if there is any weather that could endanger the mission. For example if the mission is concerned with sampling in clear sky conditions, then it might be an idea to avoid any large low-pressure systems; similarly if the purpose of the flight is to measure cloud microphysics, then prolonged expected patches of clear skies are to be avoided. The week of the flight itself is often a very nervous time for the flying team, as they hope for the right combination of weather in which to achieve their mission objectives, although as Jagger once mused, "You can’t always get what you want!" On the day of the flight itself the mission scientist will have a very detailed weather forecast, and will brief the pilots about any potential complications that could arise, determining a contingency plan if they should do so.

The Sortie Briefs themselves are then used by the mission scientists, pilots, and instrument scientists on board the flight to help guide them with their mission objectives, and then ultimately to assess the outcome of the mission in the debrief that immediately follows the flight. At first glance these 1 or 2 sides of A4 may seem like a fairly straightforward set of instructions that has been thrown together with relative ease, but I can assure you that nothing could be further from the truth!