What to Expect on Oral for Add-on Rating

iamtheari

iamtheari

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I finally finished my CPL, so now I have done 3 check rides with oral exams: private, instrument, and commercial. Those all had plenty of ground for a lengthy oral exam. Privileges, procedures, flight planning, etc.

Now, I am planning to add my AMEL rating. What should I expect for the oral exam? Same stuff as my commercial ASEL could have covered, or more focus on AMEL systems and ADM compared with ASEL?
 
More focus on the aircraft systems ,I had do draw a picture of a major system on the airplane I used for the multi. I did the fuel system from memory.
 
The table for "Addition of an Airplane Multiengine Land Rating to an existing Commercial Pilot Certificate" in the Commercial ACS would be a good place to start...

Screenshot_20201026-144948_Adobe Acrobat.jpg
 
systems and performance. My Multi add-on oral exams usually take 1-1.5 hrs. We talk about accelerate/stop/go, single engine service ceiling etc etc. Making sure you know how to use the chart but more importantly some thought on how you use the info to make informed and safe real world decisions.
 
I've been doing almost exclusively multiengine add-on training for the last few months.

At least for our most common examiner, you are not likely to be asked anything that you have already proven you know. So, he doesn't ask about flight planning or weather sources or how to contact FSS or any of that.

What he will ask about is the new stuff - and really, it's pretty obvious what the important things are:
- Vmc - what it means and factors that go into it
- Multi-engine-specific performance charts - accelerate-go and accelerate-stop, single-engine climb performance
- Multi-engine aerodynamics - why do we lose 80% of performance, why are engine failures at low altitude dangerous, what is zero side slip, why do you have to "raise the dead", etc.
- And systems of the airplane you are flying, especially those that might be different than single-engine airplanes. While everything's fair game, it would be more likely to expect questions about the fuel and electrical systems than about things like the pitot-static system.
 
iamtheari said:
I finally finished my CPL, so now I have done 3 check rides with oral exams: private, instrument, and commercial. Those all had plenty of ground for a lengthy oral exam. Privileges, procedures, flight planning, etc.

Now, I am planning to add my AMEL rating. What should I expect for the oral exam? Same stuff as my commercial ASEL could have covered, or more focus on AMEL systems and ADM compared with ASEL?
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I literally just passed my AMEL this morning. The oral was really straightforward, focused on all the forces that make twin engine flying unique, lots of VMC scenario based discussion and then some review of aircraft systems. The whole thing was probably an hour.. if
 
you've taken a lot of orals. at some point, I would think, you'd have a much better idea of what's expected of you. I just started studying for multi, it seems pretty straight forward to me what needs to be studied.
 
Systems, performance, aerodynamics, OEI stuff. The MEL add on is one of the easier ratings.
 
MauleSkinner said:
...and how totally made up that number really is. ;)
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Well it's an approximation of course, some are worse, some are better, but it works at least for explaining that it's not a 50% loss like many new students may initially assume.

This number, of course, is usually calculated as the ratio of two-engine climb vs single-engine climb with the prop windmilling. So if the plane can climb on two engines at 1000 fpm and single-engine at 200 fpm, that's considered to be an 80% loss of performance. What I always thought was funny was that mathematically, it only works if the airplane can actually climb on one engine with the other still windmilling. When I'm training in the Seminole, doing engine-out work at say 5500 MSL, then the two-engine climb rate is maybe 700 fpm. The SE climb rate is -200 fpm. So, using the same formula, I guess the twin lost 128% of its performance? That seems hard to grasp because it's just a mathematical oddity (i.e. how could it lose more than 100% of its performance?)
 
In the Duchess I found 1,000 - 1,500 ft/min climb rate on two engines.. and about 200-400 on one engine. While 80% is not an exact number, at least in my (limited, so far) experience it seems to hold true as a general rule of thumb. "common sense" might say a 50% loss, but it undoubtedly has to be more for all the reasons we already know about. Looking at the POH for the Aztec it also seems comparable

As such, the Skymaster must have more favorable single engine performance stats.. which is why I also that ME comes with a centerline thrust limitation
 
RussR said:
Well it's an approximation of course, some are worse, some are better, but it works at least for explaining that it's not a 50% loss like many new students may initially assume.

This number, of course, is usually calculated as the ratio of two-engine climb vs single-engine climb with the prop windmilling. So if the plane can climb on two engines at 1000 fpm and single-engine at 200 fpm, that's considered to be an 80% loss of performance. What I always thought was funny was that mathematically, it only works if the airplane can actually climb on one engine with the other still windmilling. When I'm training in the Seminole, doing engine-out work at say 5500 MSL, then the two-engine climb rate is maybe 700 fpm. The SE climb rate is -200 fpm. So, using the same formula, I guess the twin lost 128% of its performance? That seems hard to grasp because it's just a mathematical oddity (i.e. how could it lose more than 100% of its performance?)
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That’s exactly why I say it’s a totally made-up number. Density altitude is the biggest player, and can result in more than 100% loss of climb performance. What the AFH says is “The most obvious problem is the loss of 50 percent of power, which reduces climb performance 80 to 90 percent, sometimes even more.” obviously 128% is “even more” than 80 or 90%. ;)

but yes, it’s important to understand that it’s always going to be substantially more than the 50% of thrust that’s lost.
 
If I could just find a Champion Lancer for the check ride... "How much climb performance does this plane lose when the critical engine fails?" "How much climb performance does a glider lose when the critical wing falls off? Double that."

I'll actually be flying an Apache, so I know that single-engine performance is going to be poor and a good learning experience.

The aerodynamics of flying around with a dead engine make sense to me. I think they're interesting enough that the few complicated parts still make for an easy rating. But of course I'll find out on the other side if that guess is right.

As far as the oral, I would expect to talk a lot about aerodynamics and systems, and a bit about things like currency being measured by category and class. I'm not sure if I should expect a lot of grilling on commercial privileges, holding out, and things like that, but part of the advantage of coming right off the CPL check ride is that those should still be fresh in my mind.

jordane93 said:
We’re all counting you!
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At the next Management Council picnic, I'm going to propose that we find some way of badging Airplane! references. I'm not sure if it will be a reward or a penalty. But I'll vote for reward. :)
 
Tantalum said:
As such, the Skymaster must have more favorable single engine performance stats.. which is why I also that ME comes with a centerline thrust limitation
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Not really...in fact, a loss of the rear engine is pretty debilitating to that airplane.

the reason for the centerline thrust limitation is simply a lack of published Vmc.
 
RussR said:
Well it's an approximation of course, some are worse, some are better, but it works at least for explaining that it's not a 50% loss like many new students may initially assume.

This number, of course, is usually calculated as the ratio of two-engine climb vs single-engine climb with the prop windmilling. So if the plane can climb on two engines at 1000 fpm and single-engine at 200 fpm, that's considered to be an 80% loss of performance. What I always thought was funny was that mathematically, it only works if the airplane can actually climb on one engine with the other still windmilling. When I'm training in the Seminole, doing engine-out work at say 5500 MSL, then the two-engine climb rate is maybe 700 fpm. The SE climb rate is -200 fpm. So, using the same formula, I guess the twin lost 128% of its performance? That seems hard to grasp because it's just a mathematical oddity (i.e. how could it lose more than 100% of its performance?)
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Around here we’re going down if one is windmilling — so we’ll call it negative performance! :)
 
MauleSkinner said:
Not really...in fact, a loss of the rear engine is pretty debilitating to that airplane.
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Interesting.. rear more so than the front? How come? What are the single engine vs two engine climb differences?
 
denverpilot said:
Around here we’re going down if one is windmilling — so we’ll call it negative performance!
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We had this discussion about departing Lake Tahoe on a hot day at max gross. You are not climbing on one engine, at all.. but would you rather extend your glide, maybe even to a legit airport, or be forced to have power off landing immediately?

Assuming one can maintain airspeed somewhere around Vyse (and obviously stay above Vmc) then it seems obvious that the second engine is still a benefit, not a hindrance
 
Tantalum said:
Interesting.. rear more so than the front? How come? What are the single engine vs two engine climb differences?
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A pusher is more efficient than a tractor engine. Same 80-90% or more performance loss applies to OEI (one engine inop) operations.
 
Tantalum said:
We had this discussion about departing Lake Tahoe on a hot day at max gross. You are not climbing on one engine, at all.. but would you rather extend your glide, maybe even to a legit airport, or be forced to have power off landing immediately?

Assuming one can maintain airspeed somewhere around Vyse (and obviously stay above Vmc) then it seems obvious that the second engine is still a benefit, not a hindrance
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Depends on how high AGL it happens. :)

There’s a no-man’s-land where all the second engine can do is help you through the airport fence. Heh.

My MEI DPE and I had a long discussion about additional factors like... “Just how long is the gear in transit in this thing?” which add to the “low altitude engine loss fun”.

But anyway... the joke was about the performance percentage. It’s negative here. :) Stop the windmill you clear that fence before you’re in the field behind it ... maybe. LOL.

Yay light twins. New risks to mitigate or accept.

(Can always fly them lighter. I believe @bbchien has done some math / spreadsheet work for his twin to make sure he actually CAN go missed on an approach at high altitudes, and know he has an actual climb rate, by weight limiting his useful load. Smart stuff, making that table. Can also work an approach in terrain backward and figure out a new missed approach point commensurate with expected climb performance instead of the published missed approach point. If you can’t climb OEI out of the valley...)
 
MauleSkinner said:
but yes, it’s important to understand that it’s always going to be substantially more than the 50% of thrust that’s lost.
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Pendant Alert!

You still have 50% of the thrust (unless your engines have different thrust values from the start). Problem is that the dead engine is now producing more drag than the operating engine and the total required thrust necessary to get the same performance goes above 100% "normal" thrust. Effectively, but not literally, reducing thrust more than 50%.
 
smv said:
Pendant Alert!

You still have 50% of the thrust (unless your engines have different thrust values from the start). Problem is that the dead engine is now producing more drag than the operating engine and the total required thrust necessary to get the same performance goes above 100% "normal" thrust. Effectively, but not literally, reducing thrust more than 50%.
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No, climb rate performance is based on excess power available over that required to maintain level flight. If you have two 100-hp engines (just to simplify the math), and it requires 80 hp to maintain level flight, you have 120 hp worth of excess power with which to climb. If one engine fails, it still takes 80 hp to maintain level flight, so you only have 20 hp of excess Power with which to climb.

it’s “climb performance” that reduces 80-90% or more, not horsepower or thrust, “effectively” or otherwise.
 
MauleSkinner said:
No, climb rate performance is based on excess power available over that required to maintain level flight. If you have two 100-hp engines (just to simplify the math), and it requires 80 hp to maintain level flight, you have 120 hp worth of excess power with which to climb. If one engine fails, it still takes 80 hp to maintain level flight, so you only have 20 hp of excess Power with which to climb.

it’s “climb performance” that reduces 80-90% or more, not horsepower or thrust, “effectively” or otherwise.
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I teach this in a similar fashion, but using the VSI

Climb rate on 2 engines: 2,000 fpm
Climb rate on 0 engines: -1,000 fpm

thus, climb rate on 1 engine should be appx 500 fpm, in the middle of the two cases, or a 75% loss of positive climb rate.

I find this basic idea has been "sticky" in the brains of my pupils, then we can discuss vagaries and tweaks like feathered props and density altitudes and other goodies.
 
schmookeeg said:
I teach this in a similar fashion, but using the VSI

Climb rate on 2 engines: 2,000 fpm
Climb rate on 0 engines: -1,000 fpm

thus, climb rate on 1 engine should be appx 500 fpm, in the middle of the two cases, or a 75% loss of positive climb rate.

I find this basic idea has been "sticky" in the brains of my pupils, then we can discuss vagaries and tweaks like feathered props and density altitudes and other goodies.
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That would be what’s known as the correlation level of learning. :cool:
 
MauleSkinner said:
but yes, it’s important to understand that it’s always going to be substantially more than the 50% of thrust that’s lost.
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MauleSkinner said:
it’s “climb performance” that reduces 80-90% or more, not horsepower or thrust, “effectively” or otherwise.
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Which is it? :p

What I meant by "effectively" is this:

Let us say for the moment that we have a way of measuring, expressing, and replicating the amount of drag created by an inoperative engine. Let's call that drag 'D'.

With both engines operating normally and producing 100% thrust, you get a climb rate of XXX fpm at Vyse (just to use a reference V speed). For these purposes, the exact value of XXX does not matter.

If, while climbing at 100% thrust on both engines, you somehow toss out and additional D worth of drag, you will no longer be able to maintain XXX fpm at Vyse. The thrust required to maintain XXX fpm at Vyse will be something in excess of 100% of what you have. For the sake of argument, let's say that a D increase in drag requires 130% of the thrust you have available to climb at XXX fpm at Vyse.

Now, instead of just tossing D drag out in the slipstream, you also reduce the available thrust by 50% (you just lost an engine). Because of the D increase in drag, you still need 130% of the thrust you normally have available, but you only have 50% of normal and less than 39% of the thrust required to continue to climb at XXX fpm at Vyse with the additional D increase in drag.

In summary:
Without D, you need 100% trust for XXX fpm at Vyse
With D you need 130% thrust for XXX fpm at Vyse
With one engine failed, you have only 38.5% of thrust required for XXX fpm at Vyse, effectively (not literally) reducing your thrust to something significantly less than 50%.
 
so pedantic...

It's obvious that the aircraft's horsepower is cut in half with an engine failure (for a two engine plane losing one engine, short of some other abnormality). What's not obvious is the performance impact this has. The pilot's "end user experience" is going to be about in line with flying something that has lost 70-80% of "its power"

The VS climb performance is the best way to demonstrate that, as noted above.
 
smv said:
Which is it? :p
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”It” (as indicated by the second “it’s” in what you quoted) is climb performance, the topic of my post from which you took the quote.

“small” said:
What I meant by "effectively" is this:

Let us say for the moment that we have a way of measuring, expressing, and replicating the amount of drag created by an inoperative engine. Let's call that drag 'D'.

With both engines operating normally and producing 100% thrust, you get a climb rate of XXX fpm at Vyse (just to use a reference V speed). For these purposes, the exact value of XXX does not matter.

If, while climbing at 100% thrust on both engines, you somehow toss out and additional D worth of drag, you will no longer be able to maintain XXX fpm at Vyse. The thrust required to maintain XXX fpm at Vyse will be something in excess of 100% of what you have. For the sake of argument, let's say that a D increase in drag requires 130% of the thrust you have available to climb at XXX fpm at Vyse.

Now, instead of just tossing D drag out in the slipstream, you also reduce the available thrust by 50% (you just lost an engine). Because of the D increase in drag, you still need 130% of the thrust you normally have available, but you only have 50% of normal and less than 39% of the thrust required to continue to climb at XXX fpm at Vyse with the additional D increase in drag.

In summary:
Without D, you need 100% trust for XXX fpm at Vyse
With D you need 130% thrust for XXX fpm at Vyse
With one engine failed, you have only 38.5% of thrust required for XXX fpm at Vyse, effectively (not literally) reducing your thrust to something significantly less than 50%.
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You can’t just magically “toss” drag into the slipstream when the engine isn’t running. In fact, if you want to get absolutely pedantic (as opposed to “pendantic” :rolleyes:), the operating engine probably produces more drag than the inoperative engine because parasite drag increases with the speed of airflow, and the propeller blast produces more airflow over the good engine than the bad.

it’s not about changing drag, it’s about changing power.
 
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Airplane Flying Handbook (FAA-H-8083-3B) Chapter 12, p. 12-2:

"The penalties for loss of an engine are twofold: performance and control. The most obvious problem is the loss of 50 percent of power, which reduces climb performance 80 to 90 percent, sometimes even more."

... p. 12-3:

"There is a dramatic performance loss associated with the loss of an engine, particularly just after takeoff. Any airplane’s climb performance is a function of thrust horsepower, which is in excess of that required for level flight. In a hypothetical twin with each engine producing 200 thrust horsepower, assume that the total level flight thrust horsepower required is 175. In this situation, the airplane would ordinarily have a reserve of 225 thrust horsepower available for climb. Loss of one engine would leave only 25 (200 minus 175) thrust horsepower available for climb, a drastic reduction. Sea level rate of climb performance losses of at least 80 to 90 percent, even under ideal circumstances, are typical for multiengine airplanes in OEI flight."
 
Ryan F. said:
Airplane Flying Handbook (FAA-H-8083-3B) Chapter 12, p. 12-2:

"The penalties for loss of an engine are twofold: performance and control. The most obvious problem is the loss of 50 percent of power, which reduces climb performance 80 to 90 percent, sometimes even more."

... p. 12-3:

"There is a dramatic performance loss associated with the loss of an engine, particularly just after takeoff. Any airplane’s climb performance is a function of thrust horsepower, which is in excess of that required for level flight. In a hypothetical twin with each engine producing 200 thrust horsepower, assume that the total level flight thrust horsepower required is 175. In this situation, the airplane would ordinarily have a reserve of 225 thrust horsepower available for climb. Loss of one engine would leave only 25 (200 minus 175) thrust horsepower available for climb, a drastic reduction. Sea level rate of climb performance losses of at least 80 to 90 percent, even under ideal circumstances, are typical for multiengine airplanes in OEI flight."
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That’s 1 “rote” to 1 “correlation”. ;)
 
MauleSkinner said:
That’s 1 “rote” to 1 “correlation”. ;)
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Well, there was a lot of ambiguity and confusion in the thread over the 80%+ loss-of-climb-performance consideration for light multi-engine airplanes. Sometimes when the fundamentals are compromised, it's best to just go back to basics.
 
PlasticCigar said:
Except you hit the ground going faster and with more energy than with a single which makes it more likely that you’ll be seriously injured or die.
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Technically that really depends on which light twins you’re comparing to which singles.

There’s plenty of singles that stall faster than some of the light twins, and some are built a lot lighter and won’t be as survivable as say... something like an AzTruck.

Just a marginal nitpick.
 
PlasticCigar said:
Except you hit the ground going faster and with more energy than with a single which makes it more likely that you’ll be seriously injured or die.

If you lose an engine coming out of TVL where are you going to land other than straight ahead (hopefully taking off toward the lake)?

There is no “legit airport” you can get to from TVL without being able to climb.
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How about back to TVL?
 
PlasticCigar said:
Of course. If you take the lightest slowest twin and the heaviest fastest single...
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No. There’s plenty of examples that aren’t at the extremes.

I didn’t argue your other point, you simply didn’t need to add a false statement to it in a bad attempt to make it stronger.

People smear themselves across the mountains here in all types. Usually with all available engines running.
 
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