fire

Can somebody explain calculating holding times, and when you must divert? I ask captains often, but keep getting there answers mixed up. If it's in writing, it'll be easier for me to understand.

thanks in advance.

320ToBearz

it's a judgement call, thats why the 4 stripers get paid the "big" bucks. some companies may have hard rules written in their operating procedures though. usually fuel is looked at every 10-15 minutes in the hold.

each CA has their own different personal minimums when it comes to fuel, while the FAA minimums are strictly a dispatching function.

in general, you get to your reserve of 45 minutes of fuel in a light ifr or vfr day, then you divert. add the furthest alternate fuel to that if it is hard ifr in the surrounding area. ie, build margins into it. coordinate with dispatch as they sometimes have a better bigger picture when it comes to weather.

Highspeedclimb

Flying for a B737NG operator, we plan a landing fuel of 5000 lbs plus our alternate airport fuel, usually around 1500 lbs give or take. We burn about 5000 lbs per hour, so when our FMC reserves page tells us we are going to land at our alt. with 5000 lbs we (I) boggie. It just depends how much fuel you have when you start to hold. 1250 lbs is about 15 minutes and so on. As the previous post said it depends on the Capt as well. What I'm comfortable with might not make another Capt as comfortable.

ToiletDuck

What's the companies position on crew members making the decision to leave? Do they make you call in and ask before you hit your minimums or do you just call in and tell them. IE. You have 25min fuel before FAA requires you to divert but you want to do it now.

Highspeedclimb

You're on your own. Never been called by the CP regarding departing to our alternate with said amount of fuel, but do know someone who was called because he landed at his alternate with 9500 lbs, or about 1:45 of fuel left. This with the alternate being 18 minutes from the intended original airport. I would say he left a little early but then again I don't know the particulars. Possibly the approach was down for maint. etc...

Ewfflyer

Exactly why they are called the PIC!!!!! The final authority!!!

There are always suggested, and sometimes required, but most pilots aren't going to go to Min Fuel before they make that decision. I've landed with my 45 min remaining before and wasn't really comfortable with it, but it was daylight and clear, just a stronger headwind than predicted. Something I'll pass on next time and just get some more gas.

shackone

Just to be on the safe side, I think you had better start that divert sooner.

For Part 121 jet ops, you'll need to plan to divert with fuel enough to get to the divert location and then have 45 minutes of fuel on board. The 45 minutes of fuel is what you plan to land with...not when you start the divert.


For Fire...

Figure out what a typical fuel burn number is for your airplane when holding...figure it for 'x' amount of fuel per minute. That value will allow you to easily figure your burn while holding.

Then figure out a typical burn (in 'x' amount per minute) for cruise...the cruise, for example, that you would use when diverting from a hold to a divert/alternate. Figure out your average ground speed in miles per minute in this divert cruise (no wind). Compute the divert distance, divide this by your estimated cruise ground speed in minutes. This gives you ETE to the divert/alternate (no descent planned just to be conservative). Then multiply the ETE times your cruise burn rate to get the estimated enroute burn. Add your FAA reserve fuel to this value to arrive at the divert fuel.

For example:

Cruise burn = 100#/minute. Cruise ground speed (no wind) = 4nm/minute.

Distance from the hold to the divert/alternate = 100nm.

ETE = 100 divided by 4 = 25 minutes.

Cruise burn = 25 minutes X 100#/min = 2500#.

If your reserve was 3000#, then your divert fuel = 3000# + 2500# = 5500#.

Now, let's say your estimated holding burn was also 100#/min. You are in the hold with 7500# remaining. You want to divert at 5500#. You have 2000# to burn in the hold...at 100#/min, this equals 20 minutes of holding time before you divert.

Maybe others can add their techniques!

fire

thanks alot guys. much appreciated

320ToBearz

oops i meant get to your vfr or ifr reserve + the enroute burn to the diversion airport. duh.

shackone

Not to worry. When we give the oral examination as part of the type check, it's discouraging to see the general lack of understanding regarding reserve fuel among the candidates...some of whom have been flying Captain for several years.