2015 March 20 Total Solar Eclipse from a CASA CN-235
Irish Air Corps eclipse flight leaving Dublin (EIME) in Ireland
The point of greatest eclipse (totality phase during 2 min 46 sec) was located in the middle of the North Atlantic Ocean east of Iceland and northwest of the Faroe Islands. As weather prospects weren’t that great for the few ground-based locations, seeing it from the stratosphere was tantalizing. Svalbard was the second choice as there are quite a few clear days at that time of the year, and the fact is the sky was indeed clear on eclipse day. The Faroe Islands were the third choice as the weather there changes very quickly which is why some saw it and others didn’t. To observe the 2015 March 20 total solar eclipse, I was offering very special eclipse flights at the edge of the stratosphere (see the similar flight executed in November 2013) in partnership with AmJet Executive and Dassault Falcon Service, but also a more conventional, and nevertheless exceptionnal, flight using a private B737-700 business jet. These very peculiar flights were a great success.
Professor Peter Gallagher, head of the Solar Physics and Space Weather Research Group at Trinity College in Dublin, was given the opportunity to fly a solar eclipse experiment on an Irish Air Corps maritime survey flight out of the military Casement Aerodrome in Dublin. To optimize the optical quality of the observations from the aircraft flying at only 13,000 feet (3,960 meters), they will be able to keep the window open during the flight while still having a good chance for clear skies. Moreover the totality duration will be greater aloft than for a stationary observer. Nevertheless this scientific eclipse flight will be surpassed by the three private Falcon 7X operating at 49,000 feet (14,935 meters) in the lower stratosphere where the totality duration will be of at least 3 minutes and 50 seconds, and pushing the aircraft to its maximum speed (Mach 0.90) would bring up to four minutes. No other commercial or private flight will surpass that duration or the cruise altitude during this eclipse, and those three passenger flights will be the highest yet during a solar eclipse after the ones of the Concorde in 1973 and 1999.
Simulation of the CASA CN-235 Maritime Irish Air Corps eclipse flight
TSE 2013 eclipse flight over Kenya (courtesy of Catalin Beldea)
The nominal flight plan is built around an eclipse-viewing Totality Run (TR) constrained by celestial mechanics, aircraft operational considerations, and a need to maintain in situ flexibility to implement contingency alternatives. For baseline planning and logistical purposes we build from:
a flight altitude for eclipse-viewing of 13,000 feet AMSL,
a nominal ground speed of 170 knots,
no wind (so ground speed equal to air speed, and heading equal to course)
Detailed pre-eclipse flight planning, and in-flight execution, will incorporate and allow for the full range of possible flight levels, air speeds, and wind-vectors that may be encountered in flight to re-optimize the Totality Run in situ as may be necessary or desired.
We define the baseline Totality Run so that the aircraft velocity vector at mid-eclipse places the Sun perpendicularly to the right-side windows of the aircraft passenger cabin to provide optimum viewing and utilization through the windows. With these constraints, we compute, three key time correlated waypoints for the totality runs that define the lunar shadow intercept and crossing by the aircraft designated C2 (eclipse second contact), MAX (corresponding to the UTC instant of maximum eclipse), and C3 (eclipse third contact). C2 and C3 will also depend upon the aircraft ground speed and track (i.e., airspeed and winds aloft).
The earlier start of the pre-totality outbound leg of the Totality Run is to be defined by a pre-totality time-correlated waypoint five minutes before mid-eclipse. The aircraft is initially positioned on the MAX-eclipse intercept track at the requisite course/heading, distance, and flight-time from the intercept point allowing for airspeed adjustment in the run up to the C2 time-correlated waypoint to compensate for deviations due to actual versus predicted winds aloft (holding the MAX intercept time-correlated waypoint invariant). After C3 the aircraft will remain on the MAX-to-C3 heading for two minutes following mid-eclipse to allow viewing of the recession of the Moon’s shadow before returning back to Vágar.
The baseline flight plan presented here is of sufficient fidelity for the presumed nominal parametric conditions assumed that, if rigorously followed, will successfully result in a highly viewing-optimized and geometrically precise time-correlated mid-eclipse intercept with the aircraft located inside of the lunar umbral shadow cone.
Irish Air Corps eclipse flight team in front of the CASA CN-235
However, all timings and correlated locations, and maps presented here are valid only for the specific set of baseline assumptions used here and shouldn’t be used elsewhere. Later recomputation of the eclipse observation plan (and thus to a small degree end-to-end) flight plan, is expected and anticipated.
The Totality Run (TR) is entered nominally at the completion of a heading re-alignment maneuver with a constant radius turn onto the TR track at the requisite UTC time, location, altitude, TAS, and heading. Once on the TR track, before the start of totality at C2, small adjustments to the aircraft speed may be made to compensate for winds-aloft or turn-exit navigation errors to maintain the desired mid-eclipse flight profile.
The end-to-end, from take-off to landing, flight planning seamlessly merges into the immutable, but nevertheless tunable based on actual flight conditions, Totality Run (TR). Most critical is entering the pre-planned Totality Run exactly as specified with minimal error. Any delay and the Moon’s shadow will pass over the location where the aircraft should have been and totality will be missed. This must, and will be, be avoided with the following measures:
To mitigate against the operational possibilities of a "time-critical" take-off delay from the military Casement Aerodrome (EIME) for any reason, an earlier than time-critical wheels-up time for a central intercept at the chosen mid-eclipse intercept point is planned. This is 10 minutes.
In the event of an on-schedule earlier than time-critical, take-off, the "extra" time programmed into the flight plan to otherwise compensate for a delay must be consumed by either maneuvering enroute (executing a loop for example), and/or flying at a slower TAS to the time-critical TR start point.
Repositioning the heading re-alignment maneuver following the outbound cruise phase can be done in situ using my Solar Eclipse Maestro E-Flight eclipse flight optimization and navigation software.