Adding Driftdown Alternates to your Flight Plan

Intro

Some flights are planned with a driftdown alternate on the release that you plan to head to in the case of an en-route engine failure at a specific range of points on your journey. Often, this is written on the release in some format like “From 25 E ABC fix to 50 E ABC, go KXYZ.” It’s easy to forget where that was, and I certainly wouldn’t want to be scrolling around for it when an engine quits, so I use a mix of Point/Bearing/Distance and Fix Info in the E175 box to remind myself. This may also work on other boxes.

Point/Bearing/Distance Review and Limitations

The box lets us put custom fixes in based on an initial point, its bearing from that point, and a distance, all delimited by slashes. If we want to have a custom fix a certain distance, D, from a pre-existing fix, ABC, on our route, we can throw ABC//D either on ABC if we want it D miles ahead of ABC, or we can throw ABC//D on the next fix if we want the custom fix D miles downrange of ABC. The limitation with P/B/D is that each custom fix needs to be created in reference to an adjacent fix, so the sequence becomes important: start at the outside and work your way in.

An Example

Note: this is a made-up hypothetical. Always follow your release and applicable SOP.

Let’s say we’re flying from Seattle down to SFO, and we have a driftdown alternate of Medford (KMFR). Our release tells us that between 25 and 50 miles south of LKV, we need to head to KMFR. Before or after that, we either turn around or continue. We need to create custom fixes for those distances, and then draw lines to KMFR. Starting at the outside and working our way in:
  • Grab LKV in your scratchpad and add the bearing/distance with the 50 miles to get LKV//50.
  • Throw LKV//50 on the next downrange fix (in this case RBL at L2) to create &LKV01 (left image below).
  • Throw LKV//25 on top of &LKV01 to create &LKV02 (center image).
  • Now that you have the two driftdown gates, throw KMFR on the downrange gate &LKV01. That will create a dotted line between your driftdown gates and your alternate on your PLAN page (right image).
Next, we’ll want to redraw those lines without actually having it on the flight plan.
  • Copy the inbound (266) and outbound (100) bearings to KMFR (left image, below).
  • Put KMFR in your FIX INFO page with the reciprocal of your inbound (086) and the outbound (100) (center, below). That should create green dashed lines on top of the white ones on your PLAN page (right image, below).
  • Delete KMFR from your FPL and activate it.
Now, you should have two driftdown gates on your flight plan, and green lines pointing to your driftdown alternate. Should an engine burp when you’re inside that driftdown gate, you’ll know immediately where to go.

Conclusion

The box has several useful functions that can be combined to improve our situational awareness and help us out in critical situations. Planning driftdowns and adding them to our flight plan helps us focus on making decisions more promptly when the need arises.