Greetings fellow SkyMaster pilots:
Thinking about the double engine failure of the SkyMaster recently off Baffin Island, several thoughts come to mind.
The sort of things that commonly cause double engine failures include:
1. fuel contamination
2. fuel system icing
3. induction air icing
4. dual-engine vapor lock
5. fuel starvation
The distance from Wabush NL to Iqaluit is 652 nautical miles. According to Wunderground, surface winds were 10 knots out of the south or east, resulting in a tailwind or cross wind, not much to worry about. With 7-8 minutes to landing, they could have been at about 4500 feet when the engines stopped (the MEA for the region).
The weather at Wabush was light snow and -10 to -8 celcius. Assuming dry adiabatic lapse rate of 3C per 1000 feet, at 4000 feet they would have had temperatures of -22C, not low enough to gel the fuel. Minimum temperature at Iqaluit was -17C that day, or -29C at 4000 feet, probably still not quite enough to gel the fuel. Conditions were probably warmer than that, given the high level of moisture (enough for it to snow most of the afternoon). So gelling the fuel is improbable given the temperatures.
Cessna says to add 1% anhydrous isopropyl alcohol if the aircraft will spend much time at minus 30C or colder. Note that there is a lot of heat capacity in the fuel, so it takes a few hours to cold soak the fuel enough for it to gel.
The light snow for several hours before departure suggests the hypothesis that ice could have accumulated on the air induction system. I have never had a problem of this sort, even when flying for over an hour in ice accumulation regions (not recommended). Also it would seem improbable that the two engines would ice over at nearly the same time, especially given the assymetric configuration.
Fuel contamination would seem to be ruled out unless they had just started drawing fuel from alternate tanks, but even then you would imagine that all tanks were filled from the same source in Wabush, so the main tanks should have failed much earlier unless the contaminant was much more concentrated in the aux tanks than in the main tanks.
One other possibility is that of vapor lock. In the T337G modified that I fly, it is very common to have fuel interruption in one engine as we climb through 11,000 to 13,000 feet, especially at low fuel flows. The fuel seems to vaporize in the injector lines, even more so when the fuel flow is low as the fuel has more time in the line to vaporize due to the lower flow rate. Did the pilots turn on the low pressure fuel boost when the first engine lost power? Still, these heating effects tend to be assymetric on the front and rear engine, and would not typically result in both the front and rear engines quitting within minutes of each other after 3-4 hours of operation. The best timer of this sort are the fuel tanks themselves.
Pilots go to great lengths to match the fuel flows of front and rear engines. The fact that the two engines quit within minutes of each other provides a lot of useful information. Some SkyMasters have electromagnetic wiggle pumps for transferring fuel from aux to main tanks. I often have these freeze up on me in cold weather, especially if there is a bit of moisture in the fuel. Ice may accumulate in the pump itself (or water that freezes on takeoff). The net result is that it is common for these pumps to freeze within the first hour of operation (when you can't pump the fuel because the main tanks are too full). By the time the second hour rolls around, the wiggle pumps may be already frozen, resulting in dead fuel in the aux tanks.
Skymasters have so many tank configurations that it can be hard to determine how much fuel these main tanks had. However, based on where the engines quit, they were airborne for approximately 3 hours and 42 minutes. We should probably hear from the pilots themselves about their fuel management approach and what they observed.
Given that pilots tend to actively manage their fuel flows to keep them nearly equal, and given the short amount of time between the first and the second engine quitting, and given that fuel contamination, dual-engine vapor lock, fuel icing and induction icing seem improbable (and produce different symptoms), we should consider the possibility of fuel starvation more carefully. Such fuel starvation could of course be caused by the inability to transfer fuel from one tank to another. The pilots may be able to tell us in detail what fuel management they used, what tanks were available, and what the state of their fuel was on takeoff. From that information we might be able to learn more about the nature of the problems they encountered.
By the way, one thing I learned from reading about this experience was the essential need for good waterproof lighting around your neck (to signal the helicopter!). The best one I have found is a green laser flare from Greatland Laser. 30 mile range signaling to an aircraft at night! I am just blown away that you can actually see this pen laser from 30 miles away with the naked eye, but I believe it! Equipped has a good article:
http://www.equipped.org/rescuelaser.htm
https://www.greatlandlaser.com/index.php?productID=162
I haven't tried it yet and have no affiliation with the company.
Weather at Wabush NL(departure) the day of the ditching:
10:53 AM 14.0 °F / -10.0 °C 10.4 °F / -12.0 °C 86% 29.75 in / 1007.3 hPa 1.5 miles / 2.4 kilometers ESE 6.9 mph / 11.1 km/h / 3.1 m/s - N/A Snow Light Snow
11:00 AM 14.0 °F / -10.0 °C 10.4 °F / -12.0 °C 86% 29.86 in / 1011.1 hPa 1.4 miles / 2.2 kilometers ESE 6.9 mph / 11.1 km/h / 3.1 m/s - N/A Snow Light Snow
12:00 PM 15.8 °F / -9.0 °C 12.2 °F / -11.0 °C 86% 29.84 in / 1010.3 hPa 2.0 miles / 3.2 kilometers SE 8.1 mph / 13.0 km/h / 3.6 m/s - N/A Overcast
12:05 PM 15.8 °F / -9.0 °C 12.2 °F / -11.0 °C 86% 29.72 in / 1006.3 hPa 2.0 miles / 3.2 kilometers ESE 6.9 mph / 11.1 km/h / 3.1 m/s - N/A Snow Light Snow
1:00 PM 15.8 °F / -9.0 °C 12.2 °F / -11.0 °C 86% 29.81 in / 1009.4 hPa 1.2 miles / 2.0 kilometers ESE 9.2 mph / 14.8 km/h / 4.1 m/s - N/A Snow Light Snow
2:00 PM 15.8 °F / -9.0 °C 12.2 °F / -11.0 °C 86% 29.79 in / 1008.6 hPa 1.1 miles / 1.8 kilometers ESE 9.2 mph / 14.8 km/h / 4.1 m/s - N/A Snow Light Snow
3:00 PM 17.6 °F / -8.0 °C 14.0 °F / -10.0 °C 86% 29.77 in / 1008.0 hPa 2.1 miles / 3.4 kilometers ESE 10.4 mph / 16.7 km/h / 4.6 m/s - N/A Snow Light Snow
4:00 PM 17.6 °F / -8.0 °C 14.0 °F / -10.0 °C 86% 29.76 in / 1007.8 hPa 0.6 miles / 1.0 kilometers ESE 10.4 mph / 16.7 km/h / 4.6 m/s - N/A Snow Light Snow
4:19 PM 17.6 °F / -8.0 °C 14.0 °F / -10.0 °C 86% 29.65 in / 1003.9 hPa 3.0 miles / 4.8 kilometers ESE 10.4 mph / 16.7 km/h / 4.6 m/s - N/A Snow Light Snow