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Departures into IMC - takeoff minima

  • John.Heddles
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John.Heddles replied the topic: Departures into IMC - takeoff minima

First a question so I know where you might be coming from ... do you have any/much bugsmasher twin time ?

From a practical point of view, the only way of complying with AIP ENR 1.5, p 4.4 in an IMC OEI scenario would be to climb to the MSA within the circling area for a return to the same aerodrome and then to LSALT if intending to land at the takeoff alternate.

An admirable thought ! Now, just how might you propose to implement it for the great majority of light twin operations ?

Until you get to the larger GA twins (at reduced weight) the remaining engine either may get you to an alternate (cruise failure) or, most likely, the scene of the forced landing/crash (near the ground failure). Even on the FAR25 twin turboprop things can get very sweaty .. and that is with the (presumed) ops engineering backroom work having be done in advance. An anecdote .. many years ago, we were going out of Tennant on a track trip run in the F27 ... wet power, both engines screaming away (as the Dart is wont to do) and the climb was in the vicinity of a couple of hundred feet per minute ... had we lost one .. we had no hope of dragging it around the circuit for a recovery. On the good old Aztec (and similar) it would have been not much different to a failure in a single ...

The problem is that the good folk who introduced this stuff as an AIP requirement for lighties came from, largely, military backgrounds with little or nil light twin exposure and, I suggest, nil commercial light twin experience. The philosophy is admirable .. let's transfer some of the FAR25 capability ideas across to the poor old light twin environment ... it just DOESN'T work that way !

Now I have a reasonable amount of time on GA twins from the smallest (excluding the Cri Cri) up to (some exposure) on large piston (Commander 685 and a bit on DC3) and light turboprop and quite a few years on airline turboprop/jet. CAR3/FAR23 just is not CAR4b/FAR25 regardless of who says any different. Any expectation of useful OEI climb at anything in the vicinity of commercial weights (especially on a nice hot summer's day) on a small twin is a pipe dream and a good start to a CFIT termination of the flight unless the pilot does things sensibly on the day. Only in benign circumstances will it work out with a happy ending.

What saves the day, routinely, is that we don't have too many low level failures to put the pilot and the aeroplane to the test.

This will most likely require a reduction to takeoff weight (by off loading payload and/or fuel) to allow for the reduced climb performance in a climbing turn - not ideal I know.

I would suggest that a better wording might be ..

This will most likely require a big reduction to takeoff weight (by off loading payload and/or fuel) to allow for the abysmal OEI climb reduced even further climb performance in a climbing turn - not ideal I know.

Keep in mind that a turn is, in the first approximation, the same as flying straight at higher weight.

That being said, the charter will most likely be cancelled

Unlikely

or the pilot would be fired

highly likely in the real world of GA

either way, problem solved.

Not really. The problem's solution requires a sensible capability acknowledgement that FAR23/FAR25 twins are very different animals in a host of considerations. The higher risks associated with light twin operations is managed better by education and controlling advertising etc., which puts the idea in Joe Public's head that the Navajo charter is much the same as flying on a sked FAR25 flight. Now, don't get me wrong. Some of my favourite recollections relate to Navajo and Chieftain flying .. but I never fell into the trap of thinking that they were in the same league as the airline turboprops and jets that I flew on the day job. Another aside ... I did my Navajo endorsement on a Chieftain operated by (long departed) Murray Valley Airlines. I had done some engineering work for the owner (Leigh Bl) and we traded that work for some flying rather than grubby money. The endorsement was run by his Chief Pilot .. and, I have to say, it was as searching and detailed as the typical airline endorsement. I certainly knew what the Chieftain could and couldn't do at the end of it ...

Or sell your existing fleet and replace them with Cessna Caravans or PC12s.

and there is a LOT of merit in that idea. However, someone has to pay for it and, at the lower end of the market, that presents something of a problem.

Engineering specialist in aircraft performance and weight control.
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Carello replied the topic: Departures into IMC - takeoff minima

First a question so I know where you might be coming from ... do you have any/much bugsmasher twin time ?

Had I known how dismal FAR23 aircraft performance was when I got my multi-engine Class One rating in the late 70's I would have thought twice about departing into IMC with commercial payloads.

I have around 1000 hrs twin experience mainly in Aztec, C130, C402 aircraft - mostly flown on an IFR flight plan. That being said, I left the industry in the early 80's to pursue a more conventional career on the ground. I am now retired!

If only you could put older heads on younger shoulders

Cheers
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  • John.Heddles
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John.Heddles replied the topic: Departures into IMC - takeoff minima

Had I known how dismal FAR23 aircraft performance was

The problem is that the Standard covers a range of capabilities .. but, especially once we are in the lower weight end, blistering OEI performance is not the gameplan. Your Types (I presume C130 is a typo and you refer to C310 ?) are all of sedate OEI performance although, like you, I had great fun flying all of them in years gone past .. I was particularly fond of the old 310.

One of the general problems covering certification is that grandfathering sees the CAR3 Standards (ancient) being rolled out on the production line well after FAR23 came into vogue. The difference between the current FAR23 and the ancient CAR3 is quite significant.

when I got my multi-engine Class One rating in the late 70's

Class One .. we both are ancient chaps .. likewise, although I did my Second Class 1975, I didn't get around to the Class One for GA until a few years later..

That also explains a lot with your posts .. they are not the stuff of a new chum working his way through the exams. I was wondering just what sort of background you might have had ...

If only you could put older heads on younger shoulders

..which is one of the reasons that we olde codgers play on sites such as this and PPRuNe ... hoping that some of the frights we gave ourselves in years gone by can be passed on to the new chums so that, just maybe, some of them can avoid that aspect of the fun of flying ..

Engineering specialist in aircraft performance and weight control.
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Carello replied the topic: Departures into IMC - takeoff minima

Oops - there is a big difference between a C130 and a C310.

The C310R was my favorite - no particular reason, it just fitted like a glove.

Nice chatting to you - "live long and prosper"!
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