Bill and swh.
Swy initially offered "some operators will advocate an increase in performance CAT (eg B->C) for and aircraft for the S/E case"
This is just plain wrong. I can guess that what swh thinks he has been told, is that often (but not always!) a Cat C MDA is higher than the Cat B minima for the same approach plate.
Such thinking indicates a complete ignorance of what the plate is trying to achieve for you.
An IAL procedure is designed to get you in a position to make a successful circle- or final-approach to the desired AD/RWY. It is designed to offer a minimum margin of safety whilst you do so.
It also provides you with a 'way out' if all does not work as you would like - the missed approach. Provided that you heed the limits of the approach design.
I am sure that we would be dismayed if we read about 'some idiot tourist' that died of thirst when their rented 4WD ran out of juice in the Tanami desert, esp if said tourist had no water, no jerrycan of diesel, no epirb or RFDS HF, etc.
We would all shake our heads and say, "its sad, but those people had no business driving in the desert without knowing the precautions they should be taking."
Same with this subject.
Every pilot could expect a question like "what is the design obstacle clearance for the missed approach" in any sort of IFR renewal, ppl to atpl, single engine to six engines! Like a flash we all answer = 100' and 2.5% gradient, Jepp Terminal 3.10.1 (e) Note 2.
In this job, it is not enough to spit this stuff out on request once or twice a year to an ATO/checkie. You are actually supposed to apply this knowledge to your operation.
If you (1) knew the answer to the question above, and (2) also think that your aircraft will not be capable of making the gradient, and (3) you have not done any homework as to how you would get around this problem, then you should NOT be shooting IFR approaches.
I would put you in the same category as the unprepared 4WD tourist above. Has no business being where he/she is.
Blindly accepting 'change CAT to C' is absolute laziness. Unless of course you sat down and worked out that such a CAT C MDA resulted in a gradient of say 1.5%, and that you had also worked out that your aircraft could fly 1.5% or better.
It is not so hard, I just don't understand this inertia in other Pprune posters. For the effort seemingly expended diving into Jepps to rebut my previous post, you could have worked out the gradient your aircraft could fly single engine!
To put something positive here, lets have a look at how you might solve the problem....
Lets say that your flight manual tells you that for the weight and temp you expect at your destination, you will make about half the required 2.5% climb gradient, say 130 fpm at 100 KIAS in the single engine situation [rule of thumb: groundspeed kts x fpm = gradient of climb/descent]
The MDA for the Whup-whup NDB is say, 800'. The missed approach altitude is 2800'.
The guy who designed the NDB approach expects you to climb 2000' from the MAPt to the missed approach altitude.
But now you know your aircraft can only make just a little better than HALF that rate. So why not HALVE the altitude change, and add that to the MDA?
i.e. "My single engine MDA for the Whup-whup NDB is plus 1000', making it 1800' "?
You don't have to calculate this every time. Why not spend 10 minutes to add another rule of thumb to your book of tricks. I can remember off the top of my head that a C402C = 1000m TODR. That is, when I was working 402's in the Topend, if the strip was dry, and the temperature was 34degC or less, I did not need to refer to a P-chart. Less than 1000m, and time to open the book.
Likewise, p5-30 of the Cessna 402C Information Manual says that a fully loaded 402C at MTOW on a 34degC day at 2000' PAlt will climb at 180fpm once you have configured the aircraft for the SE climb, target IAS 104kts.
Thats 1.8% gradient when things are going well for you.
2.5% - 1.8% = 0.7%
0.7 divided by 2.5 = 0.28
Round up to increase the margin of safety.
So, the gradient 1.8% that the book says you can achieve is a factor of 0.3 less than the required 2.5% the MA procedure requires.
0.3 of the 2000' altitude gain at Woop-woop is 600 feet. That is, using single engine climb, you will be 600' short of the missed approach altitude. Add that 600' to the MDA of 800', giving you an MDA of 1400' if you are conducting a single engine approach.
So if BNE Centre reports cloud BKN010 at Woop-woop and you are sweating along with one feathered, your decisions are clearer. Divert, hold if it is lifting, or declare an emergency and shoot the approach, knowing that you are NOT assured of a way out once you descend below 1400'
Now having said all this, I am sure that it will prompt an avalance of posts saying "No, ITCZ has a cr@p way, my sums are easier/better/more accurate...."
GOOD. At least we will get some solutions being posted, instead of dismissing it as an 'airmanship' thing.