Performance Questions

[ice2x01]

Hello, I have some examinations coming up and I just wanted to check my answers to the following sample questions, my answers are in bold. Please let me know what you think.

Thank you very much

1- For the same power setting, as the speed of the airplane increases the EPR (Engine Pressure Ratio) indication:
A- Remains constant.
B- Increases.
C- Decreases.


2- Is it permitted to use reduced takeoff thrust procedure with the anti-skid inoperative?
A- Yes.
B- No.


3- Maximum landing climb limited weight is based on: -
A- L/G down, landing flaps and One engine inoperative.
B- L/G down, landing flaps and all engines operating.
C- L/G up, landing flaps and all engines operating.

--Can someone provide a reference for this?


4- In the event of engine failure in cruise, the first step is to apply
A- Maximum climb thrust to the operating engines.
B- Maximum continuous thrust to the operating engines.
C- Maximum cruise thrust to the operating engines.


Thanks again!

[Slasher]

Check your answer for Q2 - its always been Co and MEL
procedure to go balls to the wall in every jet I've flown.

(TO using assumed method with one brake deactivated is
permitted however).

[ice2x01]

I am still at a pre-simulator ground school phase at my company, we haven't received any manual that would have the required information. The materials I have don't say anything about this, so I doubt I will be questioned.

But -- What is the policy at your company? By balls to the wall I assume you mean everything functioning?

Thank you :)

[Old Smokey]

My take on the 4 questions proffered -

Question 1 - Take 2 steps back and have a very good look at the question again. The examiner states “For the same power setting” as the initial parameter in the question. Jet engines do not produce power directly, they produce thrust. The power produced is a function of speed (which, in the question, is increasing). Power = Force (Thrust) X Velocity (TAS). So, if the examiner really meant power, it will increase (at a constant thrust) as speed increases (which it is). As the examiner states “same power setting”, to achieve this you would have to deliberately reduce the thrust levers to maintain the required constant power (an unthinkable proposal) as you accelerate. So, in this case, EPR will be decreasing by your commanding the thrust levers to reduce.

If the examiner meant for the same TLA (Thrust Lever Angle), and I can only second guess him/her, EPR will again reduce as speed increases. EPR is the ratio of Pt7 (Exhaust Pressure) to Pt2 (Total inlet pressure). With increasing speed, and with all other engine parameters being equal (including Exhaust Pressure), the INCREASING Total pressure at the engine inlet due to ram, produces a LOWER Pt7/Pt2 ratio, i.e. EPR. Thus, EPR will again be reducing. (Now this is a believable and common situation, compared to the ludicrous “Same Power” scenario).

My money is on C as the correct answer.

Question 2 is Airline or Manufacturer specific. Do you mean De-Rated Thrust, or Reduced Thrust (Flex / Assumed Temp)?

There is considerable merit in using De-Rated Thrust for an Anti-Skid Inop scenario. It allows for lower V1 speed due to the lower Vmcg, and a V1 as low as possible is your best friend in an Anti-Skid Inop Rejected Takeoff. Whilst there should be no Performance constraint in using Reduced Thrust (Flex / Assumed Temp), provided that the RTOW is correctly reduced, it is undesirable to use Reduced Thrust as your V1 will be further down the Runway, closer to the end of the ASDA, and the aircraft is in an ‘Accelerate-Stop compromised’ situation with Anti-Skid Inop. Thus, many manufacturers and Operators say go ahead with a Derated Thrust Takeoff, but caution against, or prohibit Reduced thrust.

My money is on C as the correct answer (There is no C, C being “It’s Type specific or Airline Specific).


Question 3 - We agree, B is the correct answer. The reference would be in FAR/JAR 25. I don’t have a copy of these docs to cut and paste on this computer, but here is the quote from the Australian CAO 20.7.1B (Which is essentially the same as the FAR and JAR).

10 LANDING CLIMB PERFORMANCE

10.1 For the purposes of subparagraph 5.1 (c), the landing climb requirements are met if, in the landing configuration an aeroplane has a gross gradient of climb of not less than 3.2% at a climbing speed not in excess of 1.3 VS with all engines operating.

The emboldening and enlarging of the “in the landing configuration” is mine.

Question 4 is again Airline specific (with one exception), there’s no legislative requirement in this regard. In most modern aircraft where the cruise thrust limit is specified in the FMC (Which the Auto-Thrust would follow following engine failure), the default setting is customer-defined. My own operator has chosen Climb as the Cruise Thrust default limit, so that’s what the Auto-Thrust would follow subsequent to engine failure in cruise.

The one exception is where the aircraft is passing over very high terrain, and terrain clearance following engine failure in cruise and the ensuing drift-down (2000 Ft clearance), is predicated upon the best available drift-down profile to clear the high areas, that is, with MCT set.

My money is on D as the correct answer (There is no D, D being “Sit on your hands and evaluate the situation”). Putting aside the non-existent response D, the closest that we can come to a LEGISLATIVE requirement is MCT (which you’ve chosen) to cover the high-terrain drift-down case, so B is your best option.

Lots of Ifs, Buts, and It Depends, but I hope that this is of some help.

Regards,

Old Smokey

[ice2x01]

Thank you for taking the time to write out that very detailed reply. I completely understand the concept of the jet engine's thrust being a function of input pressure.

That being said, the question is not asking whether or not the thrust will increase.. rather the indication in the cockpit.

1- For the same power setting, as the speed of the airplane increases the EPR (Engine Pressure Ratio) indication:
A- Remains constant.
B- Increases.
C- Decreases.

Which I believe is the tricky part of the question. EPR is a ratio of output over input, if the input increases so will the output so therefore the indication will remain constant.

Assuming the aircraft gains speed without me altering the thrust lever, won't the EPR reading stay the same?

[HazelNuts39]

FAA Advisory Circular No. AC 25-13 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/4b385bb9e4e9c4da862569d00076acf7/$FILE/AC25-13.pdf) states (among other limitations) that takeoffs utilizing reduced takeoff thrust settings: Are not authorized when the antiskid system, if installed, is inoperative.

I think question 1 is a stupid question because the answer depends on the engine control system and auto-throttle, if installed. Older hydro-mechanical engine control systems usually maintained a constant RPM (N2) and then EPR would decrease with increasing airspeed (Mach). FADEC-controlled engines maintain whatever they have been programmed to maintain.

Regards,
HN39

[ice2x01]

Most of the sample questions and the actual questions for that matter are "stupid" -- the proper use of the English language is a rare commodity here in Egypt. And unfortunately you have to know exactly what they mean otherwise you lose points because you speak English better than they do.

I appreciate the FAA reference, just what I was looking for. Thanks for your trouble.

[Old Smokey]

ice2x01,

I noticed your very quick follow-up question earlier as I was logging off. Sorry to seem rude in not answering it, but I think that HazelNuts39 has answered it very satisfactorily.

PS, HN has correctly stated that the FAA do not allow Reduced thrust for Anti-Skid Inop. You did correctly refer to Reduced Thrust, but remember that De-Rated Thrust IS allowed by the legislation (and desirable in many situations)

Good luck with your career:ok:

Regards,

Oldsmokey

[FlightPathOBN]

I would check on the answer for question 3, the second segment is usually the critical segment, and that is gear up....

and I am sure there are many variables, but applying max thrust with engine out on a twin has some yaw issues....

this may be useful : CESSNA CITATION (http://www.airplanedriver.net/study/part25.htm)

[HazelNuts39]

3- Maximum landing climb limited weight is based on: -
A- L/G down, landing flaps and One engine inoperative.
B- L/G down, landing flaps and all engines operating.
C- L/G up, landing flaps and all engines operating.

--Can someone provide a reference for this? The reference is FAR 25.119. The 'trap' built into this question is that there is also a "Maximum Approach Climb limited Weight" (ref. FAR 25.121(d)), which is one-engine-inoperative. Most AFM's show only a "Maximum Landing Weight limited by Climb Requirements", which is the more limiting of the two.

FlightPathOBN;

I don't agree with this statement in your reference: Transport Category aircraft have two sets of weight limitations. "Certificate Limitations" such as Maximum Takeoff or Landing weight, and "Performance Limitations" such as Maximum Takeoff Weight permitted by climb requirements, or Runway Limited Takeoff Weight. These performance limitations are part of the "Certificate Limitations". These apply irrespective of the type of operation, on the basis of the Certificate of Airworthiness (ref. FAR 25.1501 and 25.1533). There are additional performance limitations due to Operating Regulations such as FAR Part 121.

Regards,
HN39

[FlightPathOBN]

HN39,

I agree there are many, very similar, terminology references...the questions are poorly worded, and I feel for the student.

I am not confirming the 'source' I provided...it appeared to be an applicable training aide.

As we know, there is a significant difference between "Certification" and "Operations"

[Sciolistes]

Q1. I know with PMC OFF in the 737, increasing speed means increasing N1. It was the same for EPR on the 737-200 simulator that I did my MCC in too. I believe the question is type independant and is asking about the fundemental characteristics of a turbo fan and not specific implementations. Therefore, the answer to Q1 is B.

Q2. There is no specific limitation in the 737 AFM (for example), but the MEL does prohibit assumed temp T/O in such cases. I am inclined to assume this is a convention and not operator specific and therefore I would answer NO, ans B.

Q3. Tricky one as it doesn't specify the performance class. But inferring from the provided options it does not seem to relate to performance class A and so I would say Ans is B. Have a look at EU OPS.

Q4. Although I disagree from an airmanship and practical standpoint, within the context of the question MCT would be the correct answer. Ans B again!