Losing an engine at altitude over the ocean is an uncommon experience, but not improbable. And when it happens to you, will want to be prepared. Operationally you can memorize what to do. But the problem with rote memorization is the added stress of "This can't be happening!" combined with fatigue, and perhaps a few months of sitting reserve and not flying, and you miss one step... the remainder of the procedures head south.
B-6088 of Hainan Airlines flying over you guessed it – the Museum of Flight last 9 March
While I'm busily studying for recurrent, I decided to dissect the driftdown procedure in hope to provide an understanding for greater recall. The process first, then the reasons why.
- Set MCT and disconnect autothrust.
- Turn off the track 180 degrees, while slowing at altitude.
- Select Green dot.
- Determine your drift-down altitude.
- At or approaching Green dot, pull for open descent.
- Turn on your lights
- Select "Below" on TCAS.
- Re-establish auto-thrust and select desired speed.
- Your goal is to minimize the descent rate. Setting MCT will provide the lowest possible descent rate until you are clear of traffic. Why do you turn off A/T? Soon you'll be selecting open descent and you do not want the good engine to go to idle. So you're getting ready.
- Turn off the airway 180 degrees. We have to get 15 miles off course to avoid traffic, and want to initially fly parallel to the course. Why 15 miles? Because for RNP10 (another plane could have a 10 mile error, plus a 2 mile offset) we could have traffic 1000 feet below, as far as 12 miles off our course. The first 90 degree turn at .80 Mach will take about 8 miles. The second 90 degree turn will take another 8 miles. Two 90 degree turns equal 180 degrees and you will be very close to that 15 miles. Adjust as necessary.
- Select green dot speed. You've already been slowing that direction while maintaining altitude... time to set the bug. This is the speed you want to fly the initial driftdown.
- Driftdown Altitude:
- PERF Cruise altitude is the maximum altitude at green dot speed.
- PROG page is REC MAX. The altitude you can fly EO LRC.
- Note: Engine out Managed speed is EO LRC in level flight, and green dot in climb and descent.
- Open Descent. Since your thrust is in MCT, this will provide the lowest possible descent rate. (If you forgot and left the A/T on, the thrust would go to idle.) If you pull for open descent prior to green dot, the plane will start down a couple hundred feet per minute, which is fine.
- Turn on your lights so everyone can see you coming.
- TCAS to "below" enables you to see traffic below you down to 9900 feet.
- Communicate. Thanks to ADS and CPDLC... life is easy. ATC com Emergency page Set ADS:OFF to ADS:ON. Similar to squawking 7700... this sends a position report every couple minutes. CPDLC you can send your intention of the altitude you're descending to as well as selecting PANPAN.
- Re-establish auto-thrust and select desired speed. Once you are off track 15 miles, you want to get below the tracks quickly so you can continue to your alternate. Thus if there is no terrain issues then you can expedite your descent below FL290... to FL280 to fly direct to your destination. You do not want to fly across the tracks at altitude. If you leave the power in MCT, you'll continue with a gradual descent and this descent will take forever. So you can re-establish auto-thrust and select desired speed to get down and on your way quickly.
Above is a photo that I had originally placed at the top of this post. One of my friends emailed me and asked me to replace this photo with the A330. But of course.
My thought is this... could you imagine any of these planes coming down on top of you? We fly over each other daily. When we have to go down... this could be an issue if we don't know what we're doing.