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?
NO
Did they have the approach still in the box?
Of course.
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.
Learning Moments
- 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.
on final approach with autopilot and autothrust off, if you apply more thrust, will the nose begin to rise? i heard that there is a natural tendency for an airplane to do that, but im not sure if it applies to an airbus.
ReplyDeleteFrom the FCTM:
ReplyDelete"If ATC provides radar vectors, the crew will use the DIR TO RADIAL IN-BND facility. This ensures:
- A proper F-PLAN sequencing
- A comprehensive ND display
- An assistance for lateral interception
- The VDEV to be computed on reasonable distance assumptions"
Cockpit... yes. What makes the plane fly? In the very basic sense... Power she goes up. Less power she comes down. Also, with the engines under the wings, visualize the added power lifting the wings.
ReplyDeleteSo, with all things being the same and you are holding your airspeed and increase the power... keeping the same airspeed, the plane will climb.
If you had power, and hold the nose level so she won't climb... your airspeed will increase.
Same for reduction. Power back + same pitch attitude (holding back pressure) = slower speed.
Power back + same speed = pitch attitude lowers... nose down.
All airplanes.
jrsanch64 ... Whose flight crew training manual states this procedure? Are you sure this is for Radar Vectors to the Final approach course of an ILS?
ReplyDeleteI would be very hesitant, on radar vectors to be inputting... DIR TO RADIAL IN-BND.
Especially when they have yet to clear you for the approach. Because, if you input DIR TO RADIAL IN-BND course... after they say turn left heading 270 (we assume this is our course) And then then say turn further left 240. You haven't truly been cleared for what your FCTM procedure tells you to do.
Then... why you would go heads down, IFR, with traffic, being at 600 meters, inside the Final approach fix, when all you have to do is maintain the course provided by ATC, then select approach when cleared for the approach?
Besides, when you're cleared for the approach you have to select it anyway... do you not?
I think less is more in this case. Fly the provided heading. Select approach when you're cleared. And don't mess with the MCDU... It's just not necessary. All heads up and paying attention.
I'm going to do a bit more checking on this. Thanks for the great comment and throwing another technique into the mix. Can you tell me what airline has this procedure?
Thank you!
I still stick to the basics "fly the airplane" and "communicate, communicate, communicate".
ReplyDeleteI've flown much less sophisticated aircraft for most of my career (Air Force and airline), so even when my captain is PNF and heads down during critical flight phases I'm not shy about saying "hey, what are you up to?" I'm no young buck, but the worst pairing is two people who aren't all that comfortable with automation and neither of them will admit it. I've got a military pension and a family, so I have no intention of flying into the ground. I have no fear of justifying a go-around to my chief pilot. I'd rather they fire me than be another NTSB write up about "he was a good guy and seemed to get enough sleep".
I left the "ancient" world of the C-141 for the equally ancient DC-9 ("give me a vector, please") and it's been a slow progression from there due to bankruptcies and mergers. As we move to newer jets I try to embrace technology, but it's no substitute for good SA and stick and rudder skills.
Great blog. I wish we could spend more time at our companies discussing issues like this.
Thank you ST. I wish we could spend more time at our company discussing issues like this too. You know, there is something fundamentally comforting when you can get radar vectors. The good old days of the classic whale.
ReplyDeleteThe scary thing is that the more automated the planes become, and the pilot force grows up with the automation... when it goes away (fails), will they know what to do without it?
Nobody should ever fear a go-around because of what management will say. It should not even be a discussion point. If the pilot flying feels it's the safest course of action, they should do it.
Thanks so much for the great comment.
is the FROM waypoint actually called PPOS?
ReplyDeleteGood question. No, the PPOS is the acronym for Present Position. It means, you are now going from your present position to the next. Since the plane needs a "from" waypoint, it makes itself one by creating it from your last position. So, in the case of PPOS... that takes place of the real FROM. The real "from" would be you're flying SEA VOR to PDX VOR. The From is SEA. The to is PDX. If you were being vectored and then cleared direct PDX, then the plane would make a PPOS to use as the anchoring point so you could fly to Portland.
Delete