When the margins get thin

Richard Collins once summed up risk management, a subject that now elicits PhD-level jargon, in four simple words: “it’s all about margins.” That seemingly simple dictum relates to almost everything pilots do in flight, including weather, aircraft performance, fuel planning, and pilot proficiency. Shave the margins too close and you’re one bit of bad luck away from an accident.

The importance of those margins was driven home for me on a recent flight in a Pilatus PC-12, when I allowed schedule pressure to reduce them a little too much, but not in the usual way. The result wasn’t an accident or even an emergency, just an abnormal situation that didn’t meet my standards for safety.

The flight

ADS-B radar
Time to get out of Dodge – but where’s the alternate?

We had planned for an early morning departure and that turned out to be fortuitous, since a nasty line of storms was headed for our departure airport just after sunrise. Luckily, we were flying away from the weather, so if we could just take off in time we’d have a pretty easy flight.

Our passengers were early and we did indeed take off in time. Dark clouds were visible to the west, but there wasn’t any rain yet and the wind was mostly calm. Right after rotation, just as I was about to celebrate our narrow escape, Murphy’s Law reared its ugly head. As I went to raise the flaps from their 15 degree takeoff position, I heard a ding and saw the FLAPS caution light appear on the annunciator panel. This isn’t that unusual in the PC-12 – the massive flaps have very sensitive asymmetry sensors that often fault when there’s nothing wrong – but you have to land and reset a circuit breaker behind the co-pilot seat before the flaps will move again. While hardly a critical safety issue, it is annoying and, most importantly, it can’t be resolved in the air.

So what was the problem? Well, we couldn’t return to our departure airport due to the advancing weather, and most of the other nearby airports nearby were covered by storms too. The only realistic option within 35 miles was a small country airport with a 3500 foot runway, trees at the end, no VASI and a decent crosswind. With the flaps frozen at 14.9 degrees and the airplane’s stick pusher system reset to “safe mode,” that would mean a fairly fast approach to prevent the stick shaker from activating. A leisurely 84-knot approach just became a 120-knot approach, and to a less-than-ideal runway for good measure.

We limped over to the airport at slow speed, limited by Vfe, while weaving around some low level scud. After briefing the abnormal approach, I ended up making a decent landing, but the stick shaker did activate momentarily on short final. It was definitely not a typical approach.

After pulling off the runway, we scrambled to reset the breaker before the weather moved in. Our first attempt didn’t work, adding to the frustration. Fortunately, a quick call to the maintenance shop reminded us that we needed to do each step in a specific order, and the second time was the charm. Note to self: good mechanics who answer their cell phones are worth their weight in gold.

We made a quick run through the checklist, then blasted off again for our destination. By now I was in a hurry because we had an event to attend on landing in Virginia, and this little stop had put us behind schedule. Since there was no parallel taxiway and the runway was a little narrow, we elected to take off the opposite direction from landing. The wind was mostly a crosswind, so it wasn’t really downwind, but we were taking off towards the trees instead of the open field. In the rush, I also forgot to put the condition lever to Flight Idle for takeoff. Again, not a critical error (the engine still develops full power and I caught the mistake a few minutes after takeoff), but nothing to brag about either.

The rest of the flight went fine, we made it to our appointment just a few minutes late and the flaps issue has yet to reappear. Still, I wasn’t thrilled with my performance on this day.

Lessons learned

A few days after this flight, I took some time to review the whole event and consider what lessons needed to be learned. After all, it shouldn’t take a near-death experience to change our habits. In fact, I sometimes wonder if we miss the subtle clues that pop up in these smaller mishaps, clues that might prevent the near-death experience in the first place.

Here are six lessons I wrote down; perhaps you have a few more to add.

Have a realistic departure alternate. A lot of instrument pilots think about a departure alternate when the weather is really low, but I’m starting to think it’s a good procedure all the time. This flight departed from my home base, so I instinctively knew the options right after takeoff, but if it had been far away from home I have to admit I didn’t consider the options well enough to make a great decision. If we had been in Oklahoma I would have been scrambling. There are dozens of reasons for a diversion shortly after takeoff; think through the options before you taxi onto the runway.

Pilatus PC-12 landing
You practice short field landings, but what about high speed or reduced flaps approaches?

Practice fast approaches more often. Private pilot training curricula spend a fair amount of time on short field landings, but zero flap (or abnormally fast) approaches are just as demanding, especially in high performance airplanes. I practice these every year during recurrent, and I’m going to give them even more attention next time. The shallow approach angle and the different control feel certainly meet the definition of abnormal. The increased distance is also significant – up to 100% in the Pilatus.

Mark up emergency checklists. It’s not wise to delete items from a manufacturer’s emergency procedures, but adding marginal notes can be a good way to emphasize key points that may not come to mind when your brain is in emergency mode. This is also useful for checklists that pertain to unusual situations that don’t show up in your POH. We have since written our mechanic’s instructions for resetting the flaps on a card in the cockpit.

Slow down when you’re out of rhythm. I know this, having learned it the hard way many years ago, and I even told myself to slow down during the flight because I recognized things were abnormal. What went wrong? I quickly forgot my “slow down” advice after landing, wrongly assuming the event was over, and missed the Flight Idle step.

You don’t need a co-pilot until you do. Flying with a co-pilot isn’t always practical, but I had one for this flight and it really paid off in a busy situation. Even if the person in the right seat isn’t a pilot, having someone to read checklists and call out airspeeds can provide a helpful reality check. One thing I was happy with on this flight was our crew resource management: we discussed the situation, considered options and thoroughly briefed the abnormal approach. If you do have someone in the right seat, take a few moments to talk about what roles they will play.

Monitor your margins. The whole episode is a good reminder that safe flying is all about having margins built in, and the status of those margins has to be continuously monitored. It’s impossible to invent, but I’d love to see a “margin meter” in the center of the cockpit instead of an angle of attack instrument, so you could know when things are getting uncomfortable. On this flight, it’s clear that the weather and the time pressure had me in a fairly tight squeeze; the outcome was positive because I had enough margins left over in the form of local knowledge, time in type, lots of fuel, and a good co-pilot.

Finally, it doesn’t hurt to have your mechanic on speed dial.

4 Comments

  • Gotta love it – Fast and Slow — two of the great lessons.

    Practicing fast approaches – it’s not just for when the flaps fail. Being able to nearly keep up when mixing in with jet traffic at bigger airports can make you the darling of the local controllers. In our Aerostar we regularly practice approaches starting at 170knots and then getting slowed down to 156knot gear speed at the marker and cross the threshold at 120knots.

    Slow down when things become abnormal. Provides plenty of time to think things through and assess other options. We use that tool often too.

    BTW, very nicely done.

  • Great story! I have to get up on my soapbox, because this is near and dear to my heart…

    The definition of professional piloting is protecting the margins. Standard operating procedures define the centerline of the safe operating space; the margins lie between that centerline and the limit of tolerable use. Best example is a runway; we track the centerline on every takeoff and landing, preserving the 75 foot (or whatever) margin on either side for any unanticipated event. No reason we couldn’t land with the right main to the left of the centerline, until we need that space for a burst tire. So everything we do is aimed at protecting that margin.

    If, in the opinion of the PIC, the margins are not adequate, he/she has an obligation to expand them…more fuel, adding a takeoff alternate, etc. Once engaged, he/she has an obligation to protect the margins, by slowing the situation down, departing the hold on the early side, ensuring a touchdown within the touchdown zone, etc.

    When pressed, a refusal to operate should not be a refusal to operate near the edge of the runway, so-to-speak, but a refusal to operate in a way that departs the centerline. Never, ever give up the margins voluntarily, even if you think it makes you look like a stuffed shirt. You don’t own the margins. Neither does the boss. They belong to the families of the people sitting behind you.

  • lesson 7…don’t accept a less than ideal runway for a non-land asap emergency. even flaps down you can outrun weather behind you.

  • John,

    Most conscientious pilots I know have flights where they’ve been frustrated by their errors and omissions even when they did not materially impact safety. Like me, they reach a point where irritation overcomes inertia and we look for the root of the problem – preflight planning, checklist discipline or something else – and correct it. What we rarely do is talk about it to anyone and my hat is off to you for doing so.

    As for activating the stick shaker, I would not be too critical. It illustrates your management of margins. Your arrival problem had two components, maintain an adequate stall margin and touch down with adequate runway remaining. I’m guessing the energy state which best accommodated those conflicting margins was quite close to the shaker speed.

    I can’t help you with condition lever!

Leave a Reply

Your email address will not be published. Required fields are marked *