This point is critical

The critical point (CP,) also called the equi-time point (ETP,) is the point exactly halfway in terms of time.

Let's say you are riding your bike to your friends house 10km away and you ride at about 10km/H. Where is the CP? Commonsense tells you it is at the 5km mark, exactly halfway between your house and your friends house.

Now let's say you are riding in the opposite direction to Grandmas house which is at the top of a big hill, again 10km away. You can ride up the hill at 6km/H, and back at 14km/H. Where is the CP? Not at the 5km mark, because it takes you more time to ride up the hill than down. We need to use the speeds to find a ratio and apply to the distance, thus;

CP = D x Vhome/(Vout+Vhome)

CP = 10 x 14/(6+14)

CP = 7km

To test, we'll see how long it takes us to ride from the CP to our destination, and how long back.

3km / 6kmH = 0.5 * 60 = 30min

7km / 14kmH = 0.5 * 60 = 30min

So here we are, riding to grandmas house, when we remember we have to call mum to let her know we are on our way to grandmas house, do we turn back and let her know, of do we ride on to grandmas house and ring her from there? Up until the 3km/7km mark, if we turn around it will take less then 30min to ride home. After the 3km/7km mark, it will take less then 30min to ride on.

This is similar to the problem that aircraft face in flight when deciding to continue on or return home in response to changed circumstances. In nil wind, the CP is exactly halfway, but if this is any headwind or tailwind (most likely) the CP will move, and it is worth noting it will move into the headwind (uphill.)

We are flying a B727 from Mount Isa to Alice Springs, a distance of 1050NM. Our cruising speed is 450kts TAS, we have a 50kt headwind and we are past the halfway mark with only 500NM to go. A passenger on board has a medical emergency. 500NM ahead of us is Alice Springs hospital and 550NM behind us is Mount Isa hospital and a whole lot of nothing in between. Do we go on or turn back? Alice is closer, but due to the ground speed difference maybe it will take less time to fly back to Isa.

CP = 1050 * 500 / (400+500)

CP = 583NM from Mount Isa (remembering the CP always moves into wind.)
or
CP = 467NM from Alice Springs.

In this case we go back.

To test, let's fly on to Alice from the CP

400/467*60 = 51min
500/583*60 = 51min.

RESULT.

Conventional

Gratz to Lex who just got the ok to fly taildraggers. I'm glad I got my qual before several thousand hours of tricycle experience made it tougher. Still, he did alright I reckon in that he got the nod after only a few weeks of non-intensive training, an hour here and there, and a false start in an underpowered Champ.

Well done mate.

Point of no return

The point of no return (PNR) is not just an expression, it has a very real meaning in aviation. The point of no return is the point at which the aircrafts endurance is enough to either go on to our destination or turn back. If we choose to go on, we no longer have sufficient fuel to return to our destination, we have reached the point of no return. On over water legs this is an important point, if there is any emergency, our choice is already made, however suitable it may be to cater to our situation, if the weather at our destination is less than ideal, a decision should be made here whether to attempt an approach or abort and go home.

Let's say we are going from point A to point C, via point B. Point B is exactly in the middle between points A and C and there is no wind. We have only enough fuel to go from A to C and no more. Where would the PNR be? It would be at point B. Point B is halfway, and at point B we would have used exactly half our fuel. Up until we reach point B we can still change our minds and go home. At point B we can go home or we can continue on to our destination. Once we've passed point B we are committed to going on to point C.

Now let's say we have more than enough fuel to go from point A to point C, but not enough to go from point A to point C and back again. This is more usually the case with commercial aircraft. The PNR is somewhere between point B and point C, but where? Confusing the situation is the wind which is a tailwind from A to C, but would be a headwind were we to turn back to A again.

And so we find ourselves at B, needing to know how much further we could fly before we reach the PNR. We have a certain amount of fuel left;

Fuel on board 14000 Kg.

And we can calculate how much fuel will be required to fly back from where we are (B) to home (A.)

Fuel required to fly back to A from B 4000 Kg

We do this and subtract it from the fuel we have on board, whatever is left over is the amount of fuel we have available to fly out to the PNR and back to B.

14000 - 4000 = 10000 Kg

If the wind was nil, we could divide by the SGR to find how many miles we could fly using this fuel, halve the distance and we would have our answer. Or to put it another way, divide by twice the SGR, the SGR out being the same as the SGR back. This is the heart of the problem - wind and different aircraft configurations mean that the SGR out is almost never the same as the SGR back. But the equation is still the same;

Fuel at B after fuel back to A is subtracted;

10000Kg

Divided by SGRout + SGRhome;

10000 / (8.5 + 10.7) = 520nm

Flight planning - headwind/tailwind

I'm studying for my ATPL and I am stuck on flight planning. In fact I've been stuck on this one subject for almost a year. For my own edification, I'm going to describe some typical AFPA (ATPL Flight Planning Aeroplane) questions, and their solutions, so I can study wherever I happen to have internet access. Perhaps some more erudite and learned ATPL pilots can happen along and give me some pointers, too.

Maximum headwind/minimum tailwind.

When flying from place to place you need to ensure that you land with a minimum amount of fuel necessary to cover emergencies. That fuel is called reserve fuel, and may not be used, except in an emergency. Using your reserves alone constitutes an emergency.

Say that I am flying a B727-200LR from point B to point C, with point A a long way behind me, and point C still a ways to go. I've already burnt up a fair bit of fuel getting here and I need to ensure that I don't touch my reserve fuel getting to point C. Aloft I can have a headwind, a tailwind, or no wind at all (unlikely.) If the headwind is sufficiently strong I may get nowhere at all.

If I am 450nm from my destination and I have 7000Kg of fuel aboard, 3000Kg of which is reserve fuel, how strong a headwind can I accept at point B and be reasonable confident of getting to point C without using my reserves? I will ignore the descent and approach for the pourposes of this problem.

Firstly, let's see how much fuel I can burn getting to point C.

7000-3000 = 4000Kg of fuel. This is my flight fuel or fuel burn off (FBO,) the amount of fuel I can use getting to point C without using my reserves.

SGR = FBO/dist. The distance to go is 450nm. 4000/450 = 8.889 This is my SGR(required) This is the most Kg of fuel per nm I can burn. If my fuel economy is worse than this, no good.

Another way of calculating SGR = Fuel flow per hour/ground speed in kts. I calculate my fuel flow from the B727 flight manual in this configuration as being 3600Kg/H.

8.889 = 3600/Gs , or Ground speed = 3600/8.889 = 404kts.

I calculate my True Air Speed (TAS) in this configuration, which is 436kts.

My Gs(req)-TAS = my allowable head/tailwind.

404 - 436 = -32 Kts. This is the maximum headwind I can accept. A positive number would indicate a tailwind is required.

I'll test this by giving myself another 2000Kg of fuel onboard to use. If my reasoning is correct, then the answer should give me a much greater accepatable headwind.

6000/450 = 13.334 SGR(req)
3600/13.334 = 269kts Gs
269 - 436 = -167 kts allowable headwind.

Let's try it the other way with less fuel. If I have less fuel to cover the same distance, then logic tells me I need less headwind, maybe even a tailwind helping me along, to get me where I am going without eating into reserves.

2000/450 = 4.445 SGR(req)
3600/4.445 = 809kts Gs
809 - 436 = 373kts tailwind required.

RESULT.

Mo Money

It's Movember, and I am once again growing a dubious tache for charity.



Frightening, hmmm?

Here is the sales pitch;

Hi,
I am growing a moustache this year for Movember. I have decided to put down my razor for one month (November) and help raise awareness and funds for men's health - specifically prostate cancer and depression in men.
What many people don't appreciate is that close to 3,000 men die of prostate cancer each year in Australia and one in eight men will experience depression in their lifetime - many of whom don't seek help. Facts like these have convinced me I should get involved and I am hoping that you will support me.
To sponsor my Mo, you can either:
* Click this link http://au.movember.com/mospace/121975/ and donate online using your credit card or PayPal account
* Write a cheque payable to 'Movember Foundation', referencing my Registration Number 121975 and mailing it to: Movember Foundation, PO Box 292, Prahran, VIC, 3181
Remember, all donations over $2 are tax deductible.
Movember is now in its sixth year and, to date, has achieved some pretty amazing results by working alongside The Prostate Cancer Foundation (PCFA) and beyondblue: the national depression initiative. Check out further details at: http://au.movemberfoundation.com/research-and-programs.
If you are interested in following the progress of my Mo, click here http://au.movember.com/mospace/121975/. Also, http://au.movember.com has heaps of useful information.
Thank you

Flying post overdue

A couple of weeks ago I took a flight to Taree with a pilot mate named Julien, whose blog you can find here. I'd been wanting to fly along the coast past Taree and back through the VFR lane for quite a while, but didn't want to do it alone, so when Julien posted on his blog that his attempt was thwarted by bad weather, I suggested we fly up together. He was PIC for the first leg, and I would be PIC for the return leg.

The weather in Sydney had been crappy for days leading up to our flight, either heavy rain or high winds, and sometimes both, but the trim Gods smiled on us and we got a window of good weather for about 12 hours on the day of our flight.

I like flying with new people, they usually have tips and tricks to pass on, and interesting tales to tell. Julien was a good choice, he is an accomplished pilot and I could tell he was a thorough planner, very organised, particular about details, all things which in almost any other endeavour would be viewed sceptically, but which are welcome attributes in an aviator. I'd happily fly with this bloke again. Julien is also pedantic about following the rules, which is something I tend to get lazy with.



We left Sydney early enough, but weren't rushed at all. No time was wasted and at no time did I feel we were in a hurry. I sat in the right seat to take these pictures. Although we had agreed on our respective roles I initially found myself handing out unnecessary advice and touching switches without asking. Naughty! In the run up bay I apologised and promised to behave myself like a good co-pilot should.



We rapidly left Sydney behind and headed north to Newcastle, still an important coal port as these waiting ships demonstrate.



There aren't too many tall buildings in Newcastle.



The shipwreck of the Sygna off Stockton Beach, an unmistakable landmark.



Ummm Broughton Island I think. My photo really does not capture its striking grandeur. The best way to see it is to barrel past at 500 feet.



Not much further north of this I saw something I hadn't seen before. A small high wing aircraft was circling low of the water. While I watched a dark whale as big as a bus broached the surface and splashed back into the waves. Sadly it was too distant and fleeting to get a photo, and Julien was on the wrong side of the aeroplane and never saw a thing.



Scenic Taree airport.



We refuelled at Taree, we didn't need to but I wanted to get an accurate idea of our real world fuel consumption. The Chief Pilot at The Manning River Aero Club had the appropriate surname of Sky, and picked it without even opening the tanks. "Forty litres per hour" he said, and he was spot on, we flew for 87 minutes and used 57 litres. 40L/H is an appropriate planning fuel consumption figure for unleaned cruise. Schofields operations manual prohibit leaning the mixture below 5000 feet AMSL. Avgas is cheap when compared to a engine ruined by an overleaned mixture. The Manning River Aero Club is a very nice example of a country flying club, very comfy and homey with a fire that must be inviting during winter.



I enjoyed sitting in the right hand seat, just watching, talking on the radio and concentrating on navigating, but I was also happy enough to be back in seat 0A.



The VFR lane is narrow and follows a railway line up a winding valley which at times is quite tight.



Williamtown military airspace is normally active above it during the week at 1000 feel amsl, and lots of the surrounding terrain is higher than that, so there isn't much space vertically either, and you have to fly low to stay legal.



After the lane it was fairly straight back to Bankstown over familiar terrain. Julien captured the landing, unfortunately a dying camera battery prevented me from doing the same for him. He was complimentary of my landing, which just goes to show how polite he is.

Lets see that from another angle

A forced landing at Bankstown airport on the 6th June 2009 captured by not one, but two cameras.





He comes down at an angle and then straightens up just before touchdown. Aircraft in one piece, passengers unhurt. Eyewitnesses say that the reason for the bank on coming in was to avoid the warehouses on the north side of the field, something Bankstown pilots have been warning about for a while now.

Bye Buddy

Yesterday around this time my wife and I said goodbye to Houston, our beloved cat, just shy of his 13th birthday.

He was my little buddy, he followed me around the house wanting to know what I was doing all day, he slept like only a cat truly can until he got hungry, then got up and ate til he was tired. He demanded to go outside just to sleep in the sun and sniff the grass, he demanded to be fed at 0545 every day. He curled up beside me to sleep just about every night.

And when he no longer wanted to do any of those things because he was too sick, he knew we would do what was best for him.

And we did, while we held him and the light went out of his eyes.

My wife has said it better than I ever could;

To others he may have just been a cat, or our pet. But to us he was our family and we loved him.

Houston, we have a problem.

I'm not even sure how to start this post.

People close to me and my wife know how close we are to our family cat, Houston. People who know how close we are will know how upset we were when he was diagnosed with cancer recently. We've been blogging our experiences as a way of coping and possibly to help anyone else out there whose beloved family pet is also diagnosed with a terminal illness. You can read how it has gone so far here.

We recently took him back to the vet to be checked up and got the news that we both knew was possible, but didn't think we would get. The treatment wasn't working, and now instead of having weeks or months of life left, he has only a matter of days before the pain and illness becomes intolerable. It was a terrible shock to us because he had been doing very well. So well in fact that the vet recommended his dosage be cut down. I now wonder if that was a mistake. Nevertheless, I'm convinced the treatment he received extended his life and that we would already be dead without it.

Anyone who has or had a family pet that they love, for thirteen years in our case, could understand just how painful this is for us. He is the closest we have to a child, and soon he will need us to do the right thing, which is end his life before it becomes too much to bear.

I don't know how to end this post.

Wolfie 2

Photos taken in Bicentennial Park and Newington Armoury by my lovely wife Kirrily.