Flight and duty times, pt 121 or sked 135

[livin'thesim]

I have a question regarding computing the sliding 24 hour window. After experimenting a lot with many different scenarios, I have begun to think that there is an easy way to compute flight time in a 24 hr window.

I believe that it is only necessary to compute all flight time that occurs in the 24 hr period before a specific flight's completion time. In other words, suppose I have several flights in a 24 hr period. The easiest way to determine compliance with the regs is to do it on a flight by flight basis, instead of a 24 hour basis.

Essentially, the algorithm would go like this.

a. Note the stop time of the flight currently being checked (Flight 'n') for compliance.

b. Add the time of the flight being checked (Flight 'n') to the total tally.

c. Check the previous flight (Flight 'n-1'), and add all time that occurs within 24 hours of the end time of Flight 'n'.

d. Repeat until there is no more flight time within the previous 24 hours.

Here is the part that I am worried that I have not figured out. Is there any way a flight can look legal if you measure from the end of that flight, but the 24 hr window would be violated somewhere in the middle of the flight?

Or is it okay to check at the end and call it good? I have tried to find an example that looks good at the end, but is illegal in the middle, with no luck.

Any help is appreciated.

 

[Joblio]

Yes, there is a way that you could violate the FARs in the middle of a flight. For example:

You have 8 hours of flying already in the last 24 hours, but exactly 24 hours ago you started a 1 hour flight. You are now legal to start flying, since you lose a minute of flight time from 24 hours ago for every minute you gain in flight time now.

However, if your current flight goes on for more than one hour, you will stop losing time from 24 hours ago and continue to gain time now, therefore putting you OVER 8 hours of flying time in the last 24 hours.

The best way to calculate it is to look at the END of the proposed flight and see if there is less than 8 hours of flying time in the previous 24 hours before that time.

 

[livin'thesim]

I should rephrase the question.

I do know that you can violate the 8 in 24 in the middle of a flight.

My question, again, is whether checking from the end of a proposed light will catch all possible violations, or do you need to do a minute by minute check from proposed flight start to proposed flight end?

In other words, my understanding is that if a violation would occur in the middle, it would also occur at the end. So that if you were legal at the end of a flight, you were legal all the way through.

If I am wrong, please show me an example. I need to solve this problem before I start writing my flight / duty program.

Thanks.

 

[Joblio]

Okay, I understand and agree that there isn't a way for you to violate 8 hours in the middle of a flight if you don't violate it by the end of that flight. Of course, that assumes no layover or break in the middle of a flight.
Good luck writing your program!

 

[livin'thesim]

That's what I thought. I spent a while with pen and paper trying to create a scenario where the flight was legal at the end but not in the middle.

It makes the computation a lot easier, really because you only have to tally all the flying occurring in the 24 hrs before the end of a particular flight.

Anyone else got an example that would shed some light on this?

 

[Mysteryofflight]

Legal to start legal to finish. If you're not legal to start the flight then you won't be legal in the middle.

 

[DrewBlows]

That's right, legal to start legal to finish. I think you are confusing rest requirements. You can only be scheduled to fly for eight hours between rest periods. You are required a minimum of nine hours of rest (reduceable to eight) between duty periods. To determine what your minimum rest is, you need to look back twenty four hours (which is rolling, so take the most hours flown in any past twenty four hour period while on duty), then figure it out based on a chart (which you should always keep with you because it's impossible to remember).

<=8 hours flight (sheduled or actual) 9 hours rest, reduceable to 8.
8.1<=9 hours flight; 10 hours rest, reduceable to 9.
9.1<=10 hours flight; 11 hours rest, reduceable to 10.
11.1+ hours flight; 12 hours rest, reduceable to 10.

I'm pretty sure that these numbers are wrong, hopefully someone can correct me.

 

[DrewBlows]

I see what you are asking.

You need to figure out what the most time (scheduled or actual) in any 24 hour look back during your duty period is and figure out your rest based on it. It's possible to figure out what your rest for the next rest period should be based on what you are scheduled and or what you fly.

Clear as mud.