Monday, 14 May 2018

SPIRALS

Acknowledgements: Thomas P. Turner (Mastery Flight Training Inc.)

(Ed. Note: Thanks Tom – another insightful piece!)

The NTSB reported last week:

“…a North American SNJ-5 airplane impacted terrain following a loss of control during initial climb after take-off from runway 13R (8,000 ft. by 200 ft.) at Kingsville Naval Air Station (NQI), Kingsville, Texas. The pilot and pilot rated passenger were fatally injured and the airplane was destroyed. Visual meteorological conditions prevailed. 

Witnesses reported that the airplane took off on runway 13R and had requested a right-hand teardrop turn for a departure toward the north. The witnesses reported seeing the airplane in a steep right bank with some witnesses reporting that the bank angle exceeded 90 degrees. The airplane descended nose low and the right bank angle lessened before the airplane struck the ground”. 

Stalls and spins get the lion’s share of coverage in instruction and in article and videos concerning Loss of Control – Inflight (LOC-I). To be sure, stall/spin events are hazards requiring this focus—the record shows that LOC-I events are the most common fatal accident scenario, and most LOC-I events appear to be stalls that often develop into a spin before impact.

There is another LOC-I sequencethat is neither a stall nor a spin. It is a natural outcome of aircraft stability, and a characteristic of all longitudinally (pitch) stable airplanes. Yet it is not mentioned by name, trained, or evaluated for or in the Practical Tests for pilot certificates or ratings. The sequence is spiral dive, and it’s what witnesses in the SNJ crash seem to describe.

Here’s how the U.S. 
Airplane Flying Handbook explains a spiral: 
“A spiral dive, a nose low upset, is a descending turn during which airspeed and G-load can increase rapidly and often results from a botched turn. In a spiral dive, the airplane is flying very tight circles, in a nearly vertical attitude and will be accelerating because it is no longer stalled. Pilots typically get into a spiral dive during an inadvertent IMC encounter, most often when the pilot relies on kinaesthetic sensations rather than on the flight instruments. A pilot distracted by other sensations can easily enter a slightly nose low, wing low, descending turn and, at least initially, fail to recognize this error. Especially in IMC, it may be only the sound of increasing speed that makes the pilot aware of the rapidly developing situation. Upon recognizing the steep nose down attitude and steep bank, the startled pilot may react by pulling back rapidly on the yoke while simultaneously rolling to wings level. This response can create aerodynamic loads capable of causing airframe structural damage and /or failure”
The AFH recommends this spiral dive recovery technique:
1.   Reduce Power to Idle
2.   Apply Some Forward Elevator (i.e., reduce the G load)
3.   Roll Wings Level
4.   Gently Raise the Nose to Level Flight 
5.   Increase Power to Climb Power 
But this doesn’t explain WHY an airplane will naturally enter a spiral or how such spirals develop.  This lack of emphasis in training syllabi and complete absence in Practical Test evaluation means many, perhaps most, pilots may be unprepared to recognize and recover from a spiral. 

So let’s delve into why I say a spiral is a natural outcome of aircraft stability; how a pilot may enter a spiral; and why knowing about spirals is important to VFR-only and instrument pilots alike. 

Stability, steep turns and spirals
Most airplanes exhibit some level of stability in at least two of the three axes. Almost all have built-in pitch stability. If disturbed upward or downward in pitch and then released, the airplane’s nose will oscillate up and down through two or three cycles before it returns to its original pitch attitude … not necessarily on its initial altitude, but at the same pitch attitude, angle of attack and indicated airspeed. 

Put another way, a pitch-stable airplane will seek the indicated airspeed (actually, angle of attack) for which it is trimmed. The G load on the airplane will increase only if the pilot resists the airplane’s natural tendency to change pitch if it gets off its trimmed speed. 
An airplane will not stall on its ownThe pilot has to actively pull against the airplane’s stability to make it stall.

Most airplanes also have some level of stability in yaw. Kick a rudder pedal and release, or hit a wind shear that yaws the aircraft, and it will wallow back and forth a few oscillations before returning to straight-ahead flight. 

Many aircraft are stability-neutral or even slightly unstable 
in roll. Enter a shallow bank and the airplane may remain banked or slowly return to approximately wings-level flight. But bank steeply enough and most aircraft will not leveltheir own wings. In fact, in a steep turn most airplanes will continue to bank progressively more steeply. This is sometimes called the overbanking tendency, the reason it may take opposite aileron input to maintain bank once established in a steep turn.

You’ve probably seen graphs and diagrams that show the relationship between bank angle and stalling speed. What’s not often well-explained is that this relationshipis only valid in level, coordinated flight. If the pilot does not resist the airplane’s tendencies and its nose drops to seek the trimmed airspeed, the G load does not increase; it increases some if the pilot applies some but not enoughresistance to maintain level flight.

What happensif the airplane enters a steep turn and the pilot provides more or less resistance than is necessary to maintain level flight? We’ll use the 60° bank example simply because we can speak in whole numbers:
  • If the pilot adds more than 2Gof resistance, the airplane will climb; and, if there is sufficient power, the airplane will enter a sustained climb. With insufficient power the wing will quickly enter an accelerated stall.
  • If the pilot applies exactly 2Gof resistance the airplane remains level. Airspeed will decrease from the drag of high angle of attack flight, so the pilot will have to add power to maintain airspeed. If airspeed increases the airplane will climb, or the pilot may reduce back pressure; more power means the same G load is sustained at a lower angle of attack. If airspeed decreases the airplane will descend, seeking to attain and maintain the trimmed airspeed.
  • If the pilot does not apply at least 2Gof resistance with elevator, power or both, the airplane will descend, seeking to attain and maintain the trimmed airspeed.

Further complicating this is the overbanking tendency. Unless the pilot corrects for it, once in a steep turn the wing will continue to bankfurther. This means the nose will drop even more. The airplane, now sensing more airspeed than that for which it is trimmed, will naturally pitch upward to return to the slower, trimmed speed. Except this pitch change is “up” relative to the airframe, not relative to the horizon. In a steep turn, this just tightens the downward spiral, increasing airspeed even more. Airspeed and vertical speed increase incredibly fast. As bank angle and speed increase, G load increases to and eventually beyond the airplane’s structural limit.

Put most simply, a spiral is a steep turn which the pilot allows to go bad!

One of five outcomes results:
  1. The pilot recovers from the spiral using the recovery technique described earlier.
  2. The airplane spirals rapidly into terrain.
  3. The airplane is high enough at the entry into the spiral that it has time to accelerate beyond VNE before it impacts terrain. Exceeding structural load limits causes the airplane to break up in flight.
  4. The pilot does not recognize the spiral for what it is, or does not know the proper recovery technique, or panics. She/he pulls back on the controls, perhaps instinctively. The G load builds and over-stresses the airframe; the airplane breaks up in flight.
  5. The pilot attempts a recovery but does not apply forward control pressure to unload the wing. The airplane exceeds structural limits in the pull-out and breaks up in flight.
Those sequences may sound familiar. One of them is usually the outcome of attempted “VFR into IMC”. The same goes for a thunderstorm or other strong turbulence encounter, even for an instrument pilot.

Frankly, I think more airplanes impact the ground out of spirals entered from uncorrected steep banks in the traffic pattern, that is, 
the pilot not doing enough because of distraction and letting the airplane do what it wants, than crash from stall/spin mishaps resulting from the pilot doing too much, i.e., resisting the airplane’s tendencies and intervening (albeit incorrectly). 

Let’s go back to our example. The pilot asked for permission to do a “right hand teardrop turn” from Runway 13 for a departure to the north. This at least suggests the pilot intended to make a fairly steep turn shortly after lifting off. It’s at least consistent with what I see at air shows all the time.

So, if a pilot plans such a departure, what does that pilot need to be thinking about?
  • “If I am going to bank 45° while climbing I will need to exceed 1.4G in the climb or the airplane will descend into a spiral entry.”
  • “If I am going to bank 60° I will need to exceed 2G in the climb or the airplane will descend into a spiral entry.”
  • “I should not exceed 60° bank in the climb because the G load required will increase exponentially and the airplane will either stall or slide into a spiral entry.”
  • “If at any point the airplane begins to descend all I need to do to recover is to reduce the bank angle and unload the wing.”
  • “Is this even a good idea at all? What are my margins, and is there any real benefit from the added risk?”

We don’t know yet if there was an engine issue, or the pilot pulled into an accelerated stall, or if there was some sort of control issue, or whether there were medical or other issues that led to the flight path that witnesses described. Whether a spiral was a factor in the SNJ crash or not, though, perhaps you know a little more about spirals and how to avoid them now because of it”. 


FLY SAFE!

Thursday, 26 April 2018

KNOW WHEN TO FOLD EM: HOW TO AVOID TUNNEL VISION IN THE COCKPIT

Acknowledgements: AIR FACTS (John Zimmerman)

(Ed. Note: Yet another great article from AIR FACTS using actual examples to help us to develop our own personal Safety Awareness - Cheers John!)

“Have you ever noticed that you become less and less flexibleas a flight goes on? Decisions that once would have been easy and stress-free become fraught when you’re close to home. It’s a natural human instinct, but it’s one pilots need to aggressively fight.

I was aware of this trap while planning a recent cross-country flight when the weather was decidedly marginal. Sitting at home, I was considering whether to cancel the flight entirely – it wasn’t unsafe to fly, but it was an ugly day, with scattered thunderstorms, potential in-flight icing, and gusty winds. After a closer look at the radar and some fresh METARs, I decided to drive to the airport. 

Once I was at the hangar, though, I almost felt locked into taking off. I was emotionally invested in my decision, and didn’t want to look unsure or timid, especially after my passengers arrived. Could I really cancel now?I could, but had to admit that it was becoming harder by the minute. Sensing a potential trap, I excused myself from the passengers to review the plan and the trip. I asked myself what I would tell a friend in the same situation who called me for advice? On the pro side, weather conditions were above IFR minimums by a comfortable margin, I was proficient in the airplane, and we would be flying towards improving weather. So I decided it was a challenging but completely safe flight, then walked back to the airplane and we blasted off. Our flight was uneventful and surprisingly comfortable, so I felt confident that I had made a good decision, but obviously some outside pressurehad crept into the process.

The same thing can happen in the air – the closer you get to your destination, the more your optionsseem to narrow. Right after take-off you might consider turning around if things look bad, and en-route you might tolerate a 100-mile deviation around weather to be sure. But within 20 miles of the airport, it’s amazing how tunnel vision can take over.

Identifying the problem
The formal term for this trap is “plan continuation bias,” a fancy-sounding phrase that nevertheless describes the problem pretty well: the more time you invest in a plan, the less likely you are to change it. Tell-tale signs that this bias is at work include statements like, “I can salvage this,” or “We’ve come this far, we can’t turn back now”. It shows up in all kinds of accidents, including fuel exhaustion and VFR-into-IMC scenarios.

One example of this bias at work involved an American Airlines MD-82 which crashed at Little Rock Airport in 1999. It was late at night and the weather was bad, with thunderstorms all around. The pilots were tired and this was the last leg of the day. As you might expect, this crew wanted to get on the ground soon, and they were very close to landing – perfect setup for plan continuation bias. So they continued their approach, even as a thunderstorm parked itself over the airport. The result was a runway overrun that killed the captain and 10 passengers.

You might think this is just another way of describing “get-there-itis,” but there’s more to it than that. A huge percentage of general aviation accidents occur during approach or landing, including a stall/spin on final, runway overruns, and ground loops – often in good weather with perfectly functioning airplanes. In many of these situations, the pilot ignores the urge to go around and tries to make the airplane land when it simply doesn’t want to, reasoning that abandoning the approach would risk public embarrassment!

A Lear-Jet accident at Teterboroshows how strong the urge is to continue an approach even when things start to go wrong. The airplane, with only two pilots on board, was flying the circling approach to runway 01, a common but demanding visual approach. Winds were gusty, but more importantly the approach was never stabilised. The co-pilot, who was flying, did not start the turn for runway 01 until the airplane was less than a mile from the end of the runway. From this point, it was almost impossible to safely land the airplane. Anyone who has ever flown to the New York area has to admit that a go around at TEB is a big deal. Of course an accident is even a bigger deal, but if ever there were a setup for plan continuation bias, this was it.

How to prevent it
Eliminating this bias isn’t possible, but there are number of strategies for minimising the threat: 
·      First, force yourself to stop periodically during your pre-flight and in-flight decision making, so you can evaluate the situation in an honest way – perhaps before engine start or before beginning your descent from the final approach fix. 
·       Is the flight really progressing according to your plan? 
·       Is your decision-making being affected by how far along the flight is? 
·       How would this read in an NTSB report?
·       The best question to ask is, “What alternatives have I not even considered?” This was the mistake I made on my flight; I was locked into a binary “go/no-go” decision, when there were other options to consider, including delaying a few hours or taking a different route. 
·      Second, it’s important to be disciplined about the regulations, and your own personal minimums. If your minimum is one hour of fuel in the tanks at landing, then you don’t go below that number under any circumstances. It does not matter that you have restless passengers on board, it’s getting late, or anything else! 

This is also where the concept of a stabilised approach comes in. You don’t have to fly a 20-mile final at Vref (unless you want the tower to yell at you), but by 500 feet AGL you should be on speed and on glide path, ready to land. If you’re not, it’s an automatic go around.

In the MD-82 accident, the pilots ignored two automatic go around cues: 
·      they lost sight of the runway 
·      the crosswind exceeded company SOPs 
Either oneof these should have caused an immediate abort, with no discussion or debate. 

That’s the critical point with minimums: the decisions have to be automatic. If you leave yourself much wiggle room, the human brain will go to great lengths to justify a deviation, “just this one time”.

Another important consideration is how you manage your workload, since tunnel vision often takes hold when you are distracted or overworked. 

In the Lear-Jet incident, the crew ended up reacting to events instead of staying ahead of the airplane. Managing workload might even require a delay vector from ATC or a turn in a hold, just to give yourself time to think.

Finally, some pilots like to plan an alternative whenever an important trip is on the calendar. This could mean packing an overnight bag (even for day trips), so there’s a little less pressure to continue when conditions change. Or it might mean buying a backup airline ticket for the return leg of a long trip. The right answer will depend on the type of flying you do, but the important point is to build some tools that help you make a more rational decision. Never sacrifice flexibility because you’re tired or rushed. And remember, it’s never too late to turn around or go around”.


FLY SAFE!