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Cross Waypoint At Or By Certain Time

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Hello everyone,

 

I was flying a flight on vatsim and the controller requested that I cross waypoint RIVET at time 0809 and at 250 knots.

 

Inputting the hard 250 knot restriction was easy but couldn't figure out how to cross the waypoint at a certain time without using RTA, which doesn't work currently in the NGX.

 

Luckily I am scheduled to cross the waypoint at the correct time. However, is there any other way to comply with this request seeing as some airlines don't use/have RTA on their aircraft?
 

Thanks in advance

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However, is there any other way to comply with this request seeing as some airlines don't use/have RTA on their aircraft?

 

Put simply?

 

Math.

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There are many ways to achieve this.

 

One is to simply reduce speed in the cruise. Reducing your ground speed until it shows that you'll cross at the correct time. Then simply increase speed to 250 when you cross the way-point. If you know the distance to run to the way point, you can calculate what ground speed you need.

 

Another is adjusting the cost index in the FMC. This will change your CRZ/DES speeds for the flight plan. This is just another way of adjusting your speed en-route.

 

Descending early can also help. You slow down the lower you go for a given IAS. But keep in mind that you also burn more fuel. So it's best to try and achieve this close to flight idle. Not my favorite option but can work if all else fails.

 

If none of the above work.... Ask for vectors or en-route holding :)

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Or just check the time overhead in the legs page 2, change the speed accordingly and manage it myself instead of the FMC.

 

You can also just put in the time they want you to be overhead the waypoint and it will adjust speed accordingly

 

I was told its quite common for oceanic crossings;

 

you get a clearance with a Mach number, and some waypoiunt crossing before or after a certain time

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You can also just put in the time they want you to be overhead the waypoint and it will adjust speed accordingly

 

I was told its quite common for oceanic crossings;

 

That is the RTA function, which the real aircraft FMS has, but which is not yet modeled in the NGX. I believe it is a feature planned for V3, but that is probably still quite a long way out.

 

As you said, the best solution for now is to monitor the predicted crossing time on the PROG page, and adjust speed accordingly.

 

You can calculate the required true airspeed by taking the number of minutes between current time and RTA time, dividing by the current distance to the waypoint, and multiplying the result by 60. That will not take the effect of wind into account though.

 

RTA for the first oceanic waypoint seems pretty common in clearances for flights heading westbound from Europe on the NAT tracks, but less common for eastbound flights from North America.

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Amazing that sometimes a bit of piloting is actually required to fly these things...  :wink:

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Amazing that sometimes a bit of piloting math is actually required to fly these things...  :wink:

 

There corrected that for you :P

 

We used to have to memorize the non-radar procedures when I was in ATC years ago. It was a lot of times and holds. It's the only way you can do sequencing if there is no radar and you are an approach controller.

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Descending early can also help. You slow down the lower you go for a given IAS. But keep in mind that you also burn more fuel. So it's best to try and achieve this close to flight idle. Not my favorite option but can work if all else fails.

 

But doesn't the TAS max out around FL260?

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Slayer, on 08 Jun 2016 - 2:47 PM, said:

There corrected that for you :P

 

We used to have to memorize the non-radar procedures when I was in ATC years ago. It was a lot of times and holds. It's the only way you can do sequencing if there is no radar and you are an approach controller.

 

By piloting, I actually infer at least some degree of mathematical ability. (excuse the pun) :ph34r:

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