To navigate, the A330 needs to have a point it’s navigating from and point it’s going to, and a line in between. We’ll call this our route. When ATC takes us off that route by giving us a heading, we now are flying in heading mode on some random course. The route is still on our map, and in the MCDU, enabling us to return to it at any time. But we’re flying some other heading into space.
Now imagine you’re off your route flying on a heading somewhere in space, and ATC tells you to fly direct to a point. Remember, the airplane needs a point it’s flying from, along with the point it’s going to, so it creates a point at your present position to anchor as a “from” point, then we can navigate to the to point.
PPOS is just the shortened version of the word: Present Position.
A330 pilots learn to clear “to” the PPOS to clean up the map and MCDU. We then learn by clearing “the” PPOS we’re able to see the lateral distance in mileage to the inbound course.
Because we don’t need all those other points on our map behind us, we “clean up to the PPOS.” Meaning, we clear out all the points we’re not using (behind us) up to the present position, the PPOS. To give us situational awareness intercepting the final approach course we then clear the PPOS, enabling us to see how far from the inbound course we are.
But before you ever push buttons, it’s imperative to know that in the Airbus world there is a time and place for everything.
So… what happened in the Shanghai flight?
A KEY A330 Learning Moment
When you clear to the PPOS, it clears the points behind you. Note: The A330 knows that you have cycled past a point if you pass it within five miles. Think about “where” the Shanghai crew was on the approach. They were being vectored “Inside” the Final Approach Fix— Locked on course and the glide-slope was just about to engage.
By clearing the PPOS, the pilot cleared all the points behind the plane’s present position, as well as their present position. Outside the final approach fix (FAF) they would have had the FAF in front of them, and could have seen the distance to the course. However, inside the final approach fix, by clearing the PPOS they wiped out the FAF (They had cycled past it) therefore they had no map display to the airport.
Did they need the Map?
Did they have the approach still in the box?
The runway was still tuned, identified and selected...
until pilot intervention.
Why did the events happen in the A330 Nightmare in the Making story?
I always like to go to the very beginning of the chain to see what triggered the events. Note: We all make errors. The key is to have procedures in place to first avoid and then help to mitigate those errors that could lead to an accident. Like most situations it takes more than one event to cause an accident.
Sequence of Circumstances
- ATC vectored the crew “inside” the outer marker. How often does that happen in instrument conditions? Never. I always say, "Never say never."
- Pilot’s were trained to “always” clear the PPOS on an approach without a clear understanding of the sequencing, and why the FAF disappeared lead to confusion.
- Trying to “Fix the problem” when it wasn’t a problem at a critical phase of flight, thus created the real problem.
- Late hour, fatigue, instrument conditions, meters, unfamiliar territory all were factors.
- Know how your airplane’s navigation system works.
- Heads up at a critical phase of flight. Not down programing the MCDU
- Button pushing needs to happen at a safe altitude.
- If you’re on the approach, and locked on, don’t touch anything.
- If the approach can’t be continued to a safe landing: Go Around.
Tip on How to Get out of Trouble if you wipe out everything and want it back.
Situation: You’re being vectored into an intercept heading and the pilot monitoring accidentally deletes one too many points and you lose everything. You are looking at PPOS, route discontinuity and blank, blank, blank.
Recovery: Type in ABC over the route discontinuity. Select lateral offset (you can't lateral offset off a PPOS thus the ABC) Select New Destination. Insert approach, and delete ABC... and you’re good to go.
However, the Shanghai story was not the place to be pushing buttons. Previous airlines I’d worked for had rules about when you could be heads down and inputting data into the box. One airline said, “Below 10,000 feet if it’s not in the box… don’t touch it.” Another company had a similar rule but, below 5000 feet. Now with our highly automated aircraft, abundance of traffic, runway changes, etc., we find ourselves programming the MCDU at lower altitudes than ever before. We become reliant on the automation.
My unwritten rule is... if you've been cleared for the approach and accepted the approach... you'd better be able to fly it with the information you programmed and verified. If you have tools to fly the approach manually without the data in the box, then do it. If you don't, then go-around.
What is your rule for when it’s okay to be heads down?
Enjoy the Journey ... Fly Safe. Fly Smart.