Engine Management and Cost

I have a few things i want to write about soon, but i thought i would go through some piston engine management, and also how we try to operate aircraft, both efficiently and operationally to try get the best results without compromising maintenance times.

I'll give a little run down into how it costing works firstly. Lets for an example use a 402. I'm actually unsure as to what my company charges per hour for their aircraft. As line pilots we just do the flying, and leave the operations and bookings to the operations staff. However, for example lets say it costs $800 per hour for a 402. Then for a flight that should hypothetically take 2 hours on the maintenance release, then costing should be $1600. So the aim of the line pilot is to try do it within that 2 hours. Usually it's pretty spot on, but sometimes other variables means you will go over. Such things as holding, or weather deviations, a go around or instrument approach etc are all things that will increase your maintenance times. Maintenance times are done in 6 minute intervals, so therefore an extra 6 minutes of flight time will equal an extra .1 of an hour to the maintenance release. When we consider that its $800 and hour, then every .1 will equal $80 saved or spent. Therefore as an aircraft operator, i do what i can to increase efficiency and do what i can to reduce my flight times.

I do this by usually doing straight in approaches where i can. Nearly every runway is east-west up here, and the wind is nearly always from the east. Most of these runways are long enough, and sealed, that even a slight tailwind doesn't pose any real problem. Unfamiliar strips, or dubious dirt strips always require an inspection first. There is a comprimise of safety and efficiency, which is where basic airmanship comes into play. I do other things such as climbing or descending to different levels to see where the best winds are. Usually going east, the winds are lighter up higher, and heading west, a lower altitude gets you the best groundspeed. The most efficient way of working out winds is talking to already departed company aircraft and seeing what groundspeed they are getting at a level, and levelling off at a lower or higher altitude and compare. Other ways of reducing track miles is requesting direct to waypoints or aerodromes. This is done frequently when we have to divert left and right of track, it becomes more efficient to track direct to the next waypoint than manoeuvre back on the original track.

So with all this in mind, engine management for piston aeroplanes plays a big factor. Big piston engines are not like turbines and you cannot just pull back the taps to slow down. There is a constant reduction of power, till you retard the throttles on landing. The aim of the game is after reducing from take-off power to climb power is that you don't actually increase the powers again, unless in an event, such as a go-around requires you to do so. This was the same from flying C206 all the way up to the C402.

Without turbo engines to deal with, the normal range on normally aspirated engines is 20 - 25" of manifold pressure that needs to be looked after. To reduce the power too quickly especially on descent will cause shock cooling which will eventually crack the cylinder heads of the piston engine. So to avoid this, and look after the engine, most companies have a standard operation procedure on how they want their engines operated and power reduced when descending. On normally aspirated engines, we keep them full throttle till around 6000ft, which equals roughly 23" of manifold pressure. We keep them at 23" which is about an inch of power every 500ft - 1000ft worth of descent. This equates to an inch of manifold pressure every 1 - 2 minutes. When we are through 3000ft we reduce it to 21" of manifold pressure and reduce it again through 2000ft, back to 19". From there it is pilots discretion to keep the constant rate of descent and power reduction smooth and consistant till retarding the powers on landing.

This gives you a rough idea of how we operated the singles and baron's. Using this method we avoid shock cooling the engines, and also keep our speed up until near an aerodrome, which helps reduce flight times, without being detrimental to the aircraft engines.

So i will now talk about the engine management in the turbo engines. It is much the same philosophy as the normally aspirated piston, but with a much higher manifold pressure. The C402 cruises at 29" of manifold pressure. So we keep a constant rate of descent of 500ft. When we go through 3000ft, we reduce the power 2 inches, back to 27". Through 2000ft, we reduce it back to 25". This is actually where the turbos cut out, so its essentially back to a normally aspirated engine at this point. It is still important to give it a minute or two at 25" though for adequate cooling and adjusting. (on this note, if your descent rate happens to be higher, either to catch profile, or because you had to descent later, then obviously you would reduce the powers a little earlier to keep the 2 minute spacing between power changes.) In the C402 we keep the powers at 25" until we are gear down, full flap, pitch full fine, mixture full, and then start reducing the powers till retarding them for landing. Once we have landed, we also need to allow a minimum of 3 minutes for the turbo engines to cool on landing. For this reason i nearly always use the entire runway and backtrack (when operationally available) so during the cooling phase the aeroplane is always moving. I have discovered passengers hate sitting in a stationary aeroplane with the engines running, but if im taxiing around after landing no one really minds. So i always try use the entire 3 minutes just backtracking and vacating the runway. Doesn't always work, and in Darwin the taxi to the General Aviation ramp is about 4 minutes, so in some cases it doesn't pose a huge problem.

Hopefully this makes sense to all you readers. If you have any questions please ask, just a little insight into how i have been taught, and am expected to operated company aircraft. Im actually starting on the C404 soon, which is a little different with engine management from the C402, as it cruises at 31" and has turbo, geared engines, which are quite sensitive to shock cooling and have to be looked after more diligently than the C402.


Thanks for reading.

Flying to Umbakumba

I think thats how you spell it. I will just call it umk for the purpose of not writing its full name. Umk is one of the few strips i have been into, when i was flying singles that i stuck out as being dodgy, short and with crazy cross winds. Its right on the coast, on Groote Eylandt, roughly 40km north-east.


I remember the first time i went to the strip, was in a C206 with a whole bunch of computer equipment. It was during the dry season, and i have a horrible headwind the entire flight. Now the flight to Umk is 357nm. Couple this with about 2 months of solid baron flying, then going back into the slowest 206 on one of the longest flights, i was not a happy camper, as such. Anyway, i remember arriving at the strip and the wind was easily around 25-30 knots, all cross. Even though i have over a 100 hours on C206 aeroplanes, it felt foreign since i hadn't been flying it as recent, and it doesn't take long to lose your feel for it.

So we arrived and it was one of about 3 times in my flying career, where the only thing i was thinking was "this could go either way." Not a very good feeling! I remember as i landed with full aileron into wind, and full rudder i was still being dragged across the runway. Eventually i stopped and backtracked, uneventfully, but that was my first memory of that strip.

Fast forward to yesterday and the day before, im told im going to umk in a C402 with a lot of gear for a few blokes who are overnighting. So we departed just before first light and did the 357nm, reasonably slowly at 9000ft, and arrived at a very calm umk, no wind, and the strip looked and felt better than i remembered! So not to worry. Unloaded and was asked if i was picking them up tomorrow! Naturally i had no idea i would be, but as it turned out, i was doing the return charter.





Umk from the air and from the ground. These were taken at about 8:30am on the first day dropping the boys off.

Now the return charter was bumpy being in the afternoon with lots of build up happening. But none the less, arrived over Groote Eylandt and saw no less than 3 cells around the umk areas. It was rough while descending, and i even reduced power early to try give the least impact to my mid 70's built chariot. Did a solid circuit over the strip to make sure i knew where the wind was coming from and did an uneventful and windless landing?! Again, i was suprised, but all was good.

Now for when we finally departed, those little areas of buildup were now a solid line of storms. Every time i thought i found a gap, all i could see was huge amounts of lightning and more cells behind them. I think i ended up diverting 20nm to the north and eventually found a gap. Even though i had weather radar in this aircraft, i found it was actually easier and most likely safer to remain visual and go lower/find the gaps. Worked well, and after about 20 - 30min of storm dodging we were in reasonably clear air with just isolated cells around, but none on my track to Jabiru for my fuelling stop. I needed fuel, mainly due to the holding requirements back into Darwin, but i had also done a few extra stops on the way to umk, combining 2 charters into one, as i was empty over there, it made operational sense. One was to Bickerton Island, and the other to Ngukkur.



Line of cells i was dodging about 20 minutes into the cruise. I was tracking virtually north at this point for around 20nm to get around them.

So we eventually arrived at Jabiru, and although being a reasonable sized airstrip for Arnhem land, it has no lights, but the fuel there is a lot cheaper than elsewhere... when it works! Since it has no lights, and i landed at around 18:15, that gave me roughly 45 minutes till end of daylight for departure. Not a problem to put 300lbs of fuel on a 402. But as it turns out Jabiru had been hit by a massive storm about an hour earlier, which after a few calls found out had busted the bowser. Luckily i know a few of the boys that work for the local companies in Jabiru and was able to get one of them to come out and try reset the switches. Eventually it worked, and we were airbourne at around 18:55. Close! The last thing i wanted after such a big day of flying was to overnight in Jabiru!

Flying over Kakadu National Park at 6000ft on the way to Jabiru for fuel. The terrain in this area is around 2500ft.

Anyway, thats the story of yesterdays adventure. I'm going to write more about "how is this going to end" in a future post. I have some good stories, and weird occurances that have happened, mainly doing mailruns in central Australia. Most times it's been external factors, that was happened, but its crazy just how quick you can think and remember things when you have too. till next time, enjoy some of the photos!

I have also uploaded a video of me landing a C402B into Maningrida. Enjoy. http://www.youtube.com/watch?v=gz1ibW3W_WM



On the back of a ute at Bickerton Island. Good times.

Numbalwar from the air! You can see the strip on the left hand side.

YTTI

Troughtn Island, or YTTI, was a place i always wanted to visit. I don't know why i did to be honest, but the idea of landing on a small strip in the middle of nowhere. Literally all the island has is a 980m coral strip (with PAPI!) and a few donga's/a hangar. There was also a ute that was missing its doors. Good times.


http://www.shorelandsgroup.com.au/images/troughton2.jpg - That may be a better idea of the place.


I flew out there to take a few guys fixing the meteorology station out there. Troughton is run by the Shorelands group, and i believe its used as an alternate for all the big offshore oil rigs out in the Timor Sea. Truscott is the main airport nearby, only around 30nm away.


There was about 25kts wind, virtually all crosswind. Max for the C402 is 20kts, so it was definately an interesting landing. In my eyes it was a good landing, but im sure my passengers were convinced otherwise haha. With lots of drift, on a short strip such as this, all i wanted to do was get the plane down on the threshold with the into wing low. Bit of a cruncher, but i pulled up in around 600m and in my eyes thats what mattered. Flight to and from was uneventful, just all over water, lots of cloud and rain, but no real weather as such.


Anyway to make this charter even better, the moment we landed we were offered a coffee, which was well needed and 'deserved.' Maybe not deserved, but very much appreciated. Then we were made big chicken salad rolls, and all sat around chatting for a long time. Signed the visitor book and saw that a lot of my colleagues have also had this pleasure!


All in all, was a great charter, one of the few that makes me so happy for my experiences working in general aviation.

The coral strip, looking south, towards the Australian Mainland.