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## Calculation PNR

• boeing777mark
• Topic Author

### boeing777mark created the topic: Calculation PNR

Hi guys

Just wondering if you guys can explain to me what does asymmetric TAS mean and also asymmetric fuel flow mean.

I am working on the question on page 7.12 in the cpl performance.

Cheers

• Posts: 1961

### bobtait replied the topic: Re: Calculation PNR

Asymmetric operation relates to a multi engined aircraft's performance after an engine fails during flight. The failed engine is feathered and secured and the remaining engine/engines are running at increased power to compensate for the loss of thrust.

Having said that, no question in a Day VFR CPL exam will ask you to calculate a PNR or ETP based on asymmetric performance simply because it is not in the syllabus. If you see any mention of asymmetric TAS or Fuel Flow, simply ignore it. The examiner as included that information as a distraction. All PNR and ETP questions in the CASA CPL exams will be based on normal operation.

Bob

• Posts: 1169

### Richard replied the topic: Re: Calculation PNR

Hi Mark,

The asymmetric TAS is the TAS you can expect to achieve from a twin-engined aircraft (such as the Echo) with one engine failed. Similarly, the asymmetric fuel flow is the fuel flow to be expected when operating with one engine out.

Cheers,

Rich

EDIT: Aha! Bob beat me to it. Hope you're getting over your flu mate!

• boeing777mark
• Topic Author

### boeing777mark replied the topic: Re: Calculation PNR

Hi Rich and bob

Thanks for your reply, I am also having trouble on knowing When you are travelling towards the PNR or away how do you know if it's a head wind or tail wind, I know the questions mentions if it is a tail wind or headwind but still seem to be getting confused.

Kind regards

• Posts: 1169

### Richard replied the topic: Re: Calculation PNR

Headwind or tailwind will be given to you and it will normally be for the outbound direction i.e. from origin to destination

If you have a headwind outbound, you will have a tailwind inbound.
If you have a tailwind outbound, you will have a headwind inbound.

In real life you would simply use the groundspeeds from your flight plan since they already incorporate the effects of head and tailwind.

Cheers,

Rich

• boeing777mark
• Topic Author

### boeing777mark replied the topic: Re: Calculation PNR

Hi Rich

Thanks for you replys, i am currently working on Q4 of the CPL Perdomance on page 7.12 and again i am geting confused as to were the tail wnd is coming from. The answer is showing 160-30= 130,now i understand that there is a 30 kt tailwind but is this meaning that they have taken of with a 30kt tailwind as the arrow is showimg to the right of the page, as the answer time to bravo is 160 + 30 =190 so is that meaning it a tailwind to bravo and a headwind back to alpha, seem to being geting a little confused ....

• Posts: 1169

### Richard replied the topic: Re: Calculation PNR

Hi Mark,

First off, which page are you on in the book? The current edition doesn't have a page 7.12. Are you perhaps referring to Q4 in the ETP/PNR questions on page 4.50?

Those questions state you have a 30kt tailwind forecast for your flight from Alpha to Bravo. This means you will take off from Alpha (obviously using some into wind runway) and, once you get cruising to Bravo, you will have the bonus of a rather pleasant 30kt tailwind to speed you along. The performance data states your cruise TAS is 160kt so your ground speed with a 30kt tailwind will be 190kt.

However, if you now turn around and start flying back towards Alpha again, your 30kt tailwind is now a 30kt headwind. You've reversed direction and are flying into the wind now. Your groundspeed back to Alpha from the point where you turned around is going to be much slower: 160-30kt = 130kt.

Cheers,

Rich

• boeing777mark
• Topic Author

### boeing777mark replied the topic: Re: Calculation PNR

Hi Rich

Yeah I am working on the ETP/PNR questions and referring back to Q4 it's is stating that there is a 30kt tail wind so I am just confused when departing alpha is there going to be a head wind or tailwind. Have great difficulty with these question ATM

Cheers

• Posts: 1169

### Richard replied the topic: Re: Calculation PNR

In this question, the 30kt tailwind refers to your flight outbound from Alpha i.e. after departing Alpha you'll have a tailwind all the way to Bravo.

Cheers,

Rich

• boeing777mark
• Topic Author

### boeing777mark replied the topic: Re: Calculation PNR

Thanks a lot for your reply Richards, appologies for the late thanks

Cheers
Mark