Discuss the problems and solutions to all of the situations that Pilot X finds himself in.
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By G-BLEW
#979407
Pilot X is a retired airline pilot who enjoys passing on his skills to new young pilots…


Pilot X wasn’t the type to rely on anecdotes and memories for his flying fix, even though he had more than most flyers could dream of. At an age when many of his former colleagues had retired to their gardens or found their excitement dangling a fishing line off a riverbank, Pilot X still enjoyed every hour of his flying days. OK, yes, he might no longer be at the controls of fast jets and airliners, but his instructing job at the local club held a particular appeal, a sense of being involved at the grassroots and even giving something back to the pastime that had served him so well.

Today his aircraft of choice was a humble C152, a classic little two-seater that had seen so many pilots through their early training. Today the Cessna was reserved for two, possibly three training flights, as long as the weather held out and he wasn’t caught up with too much paperwork. Unlike some of the other instructors at the club, Pilot X wasn’t desperate to rush from student to student more intent on racking up hours than service – probably just as well really with the general downturn in the amount of students seeking flying lessons.
Today, he was looking forward to a mixed bag of exercises, starting with a young student, still in his teens, who worked hard at the local Tesco during the week to fund his pilot training with a plan to follow a career as an airline pilot once his PPL was complete. Pilot X had taken a particular liking to this student, impressed by his determination and dedication. He was now almost at the stage of going solo and, for Pilot X, it meant just a few more circuits under his careful eye with the plan that next week would bring the big day. His exercises with that student went well.

The second lesson of the day was to have been a cross-country navigation exercise but just after the student turned up, the lesson had been delayed by a particularly vicious downpour. In fact, the shower was so sudden that the aircraft had been caught at the pumps, with the pilot still refuelling despite the incoming thunder and lightning. Ignoring the rain, Pilot X dashed over to the pilot, yelled an explanation including words such as “lightning strike” and “burst into flames”, and quickly helped push the aircraft away from the pumps before he returned to the warmth of the clubhouse.

Experience counts

By the time the storm cleared it was well into the afternoon and any hope of squeezing in a flight with the third student was well gone. What’s more, the student due to make his cross-country had been called away. Still, all was not lost. A young pilot halfway through his instructor’s course was keen to fit in some stalling and spinning practice, so Pilot X sent him out to preflight the C152 while he dealt with the call of nature. Once out at the aeroplane, Pilot X asked the young pilot whether the preflight had been completed OK before suggesting that a protracted engine run might be a good idea. He also made sure that the student had checked the tanks, including a visual check of the fuel sample. The pilot said yes, he had, and that everything was fine, with both tanks showing just over half full. With the engine soon ticking over and the gauges showing everything in the green, it all looked fine, and within a short time, the little two-seater was climbing effortlessly away from the runway, climbing up to and beyond 5,000ft.

No matter the hours in his logbook, Pilot X still loved this environment and was in his element as he explained the lesson to the student, who was preparing to repeat it back to the more experienced pilot in the near future. At 6,000ft above sea level and 5,000ft above the ground, X levelled the aircraft and ran through the HASELL checks. He had been taught to fly when spinning was a real hazard so had practised it relentlessly. OK, modern aircraft were far more stable and easier to recover, but that didn’t mean the old skills could be left to go to waste. Sadly, this didn’t appear to be an opinion shared by some younger pilots, who seemed less concerned with sharpening such skills. One result of this was that when they were faced with a situation when such skills needed to be displayed, their confidence wasn’t what it should be. To help them, Pilot X was determined to demonstrate to his charges that, provided you approached the exercise with the same level of preparation as any other aspect of flying, it should be no more challenging or dangerous.

As the 152 slowed through 50kt, Pilot X pulled back on the control column and applied full left rudder. The aircraft pitched nose-up and then rocked to the left. Pilot X kept the calm patter going, pointing out the incipient stage and then explaining the importance of holding the pro-spin controls in position to let the spin develop. Casually and calmly he pointed out a feature on the ground, using it to count the number of rotations and, as the aircraft completed the fourth, he applied the anti-spin controls, talking through his actions as he did so. He checked the throttle was fully closed, checked the direction of the spin and then applied full opposite rudder.
Holding it for a second he gently pushed the control column forward and waited for the aircraft to recover into a steep dive. Nothing happened and Pilot X casually remarked that sometimes things took a little longer to take effect than others, remarking that occasionally the spin would tighten before recovery. After two further rotations, X stopped talking and reapplied pro-spin controls before meticulously going through the spin recovery technique again. Still nothing.

The aircraft had now descended through 2,000ft with no signs of recovery. It was now that Pilot X’s many hours of experience proved their worth. He reapplied the pro-spin controls for the third time, only on this occasion applying full pro-spin aileron. As he applied the anti-spin controls, he simultaneously snapped the aileron in the opposite direction and… hoped. The little Cessna snapped out of the spin and Pilot X calmly and gently recovered the aircraft to level flight.
“I think I know what the problem is here,” Pilot X casually commented. “First off, let’s go back to the airfield and refuel.” ν


1 What may have caused the aircraft to stay in the spin despite the application of anti-spin controls?
2 Why did Pilot X choose to use the ailerons to help recover the aircraft?
3 For aircraft such as a 152, what is a safe height to enter a spin?
By AlanC
#979949
Sounds like a fuel imbalance, coupled with relying on the gauges.
By AttorneyAtLaw
#980293
The problem is not fuel imbalance as the text says that the fuel was checked and both tanks were just over half full.

I suggest the problem was too little fuel, pushing the centre of gravity too far forward. However, that would tend to make the aircraft more difficult to spin and more likely to enter a spiral dive. Is that what in fact happened here?
By profchrisreed
#980331
1. This was a prolonged spin (4 turns), and some aircraft will flatten the spin after a certain number of turns. Recovery from a flattened spin takes longer.

2. A rearward C of G inceases recovery time - no idea what might have caused that as I only fly gliders, but maybe light student + something to do with the fuel (we're told a lot about the refuelling, so is it relevant)?

3. (1) or (2), or a combination, might require more forward elevator for the spin to stop. Did Pilot X mover the stick forward all the way to the stop, or merely to the point where he expected recovery?

4. Pro-spin aileron tends to steepen the spin, and recovery from a steeper spin is easier/quicker.

I've been there in a glider, spin recovery not working, though for different reasons. In my case the areodynamic forces fooled me that I had applied full opposite rudder, whereas in fact there was another inch of travel. Experience in the manoeuvre certainly helps, because my only thought was "Can't have done that right, try again".
By AlanC
#981034
True, a fuel check was done - I would however be cautious of how it was done though, the gauges can be interesting on 152s... I would be interested in how the tanks were level when a previous refuelling had been interrupted unless I had more data. Spinning them with half tanks/less and 2 POB is a perfectly sensible way to do it, so unlikely to be a M&B issue. The main data point I have for that conclusion though is the FI's comment of refuelling the aircraft before completing any further flying!
By caber0
#983214
I think this is fuel imbalance. In the spin the inner wing being heavier will affect the centre of the spin as this will be tending toward the C of G. Recovering will be difficult. Tilting the aircraft inwards will bring C of G back towards the centre of the aeroplane and quick reversing of ailerons during recovery will give more impetus to lift the heavy wing to a point where a normal recovery will commence.

As to point 3 is a 152 cleared to spin? I guess the Aerobat version may be but I suspect the standard one isn't. I fly a 172 and it is not supposed to be permitted to spin beyond the incipient stage.

Unless the tanks were dipped prior to flight there is no certainty of the quantity in each tank. The student pilot may have omitted this in the walk around or if the total fuel still seemed good may not have mentioned to the instructor that there was a significant difference in tank loading. My experience of Cessna fuel gauges is that for all the accuracy they show they might as well have INOP printed on them in the factory:) As the fueling procedure had been interrupted it is highly likely that only one side had been filled or the second side was only partly filled.

Caber:)
By AttorneyAtLaw
#983696
Tilting the aircraft inwards will bring C of G back towards the centre of the aeroplane


I don't see how this is going to affect the centre of gravity. the only think which will affect CoG is a movement of mass in the aircraft, either fuel in the wings or crew in the aircraft!

Re-reading the piece, I wonder if in fact there was too much fuel rather than too little. Was a W & B done and was the C of G inside the aerobatic envelope? The in-spin aileron would be the sort of imput necessary to steepen a flat spin before applying recovery imputs.
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By KNT754G
#983941
Doubt it can be too MUCH fuel as the instructor wants to go back and refuel.

In spin aileron will not, as you say, move CofG, but could alter centre of rotation to bring it closer to CofG?
By caber0
#985209
Yes I meant bring centre of spin closer to C of G
Caber
By nschmidt
#985214
To me it also looks very much like fuel imbalance, judging by all sorts of emphasis on fuelling in the article:
  • Interrupted fuelling, what do you expect: the two tanks are usually filled one after another, not at the same time.
  • Pilot X did not request a visual inspection of the fuel levels. He insisted on checking fuel samples, which is very sensible after refuelling under heavy rain. This could have distracted him from specifically asking that the fuel tanks be inspected visually as well.
  • The student was reluctant to climb onto wet wings with a dipstick and wet his shirt. He probably just checked the gauges while Pilot X wasn't there.
  • Had there been anything wrong in the student's preflight report, Pilot X would not have gone spinning. So the preflight looked right from the student's words. Probably, the problem must have been with the way the checks were done.
  • After recovery, Pilot X decided to refuel before continuing the exercise -- something was wrong with the fuel.
An aeroplane approved for spinning would have been spin-tested at the extremes of its Mass and Balance envelope. (I don't recall seeing any M&B restrictions for spinning in the C152 POH.) However, this envelope is only specified along the longitudinal axis. As there are no lateral specifications, there is no need to spin-test her with fuel imbalance. Besides, with the C152's lack of separate left/right fuel tank selectors, fuel imbalance may be considered too uncommon to be tested for.

With 2 POB and no luggage, the CofG would have never been outside the safe limits longitudinally. At worst, the aeroplane could be slightly overweight -- not with half-full tanks, but we don't trust those gauges, -- but that would contradict the decision to refuel. So it's not about the total quantity of fuel -- then it must be about its lateral placement.

There was also something in Cessna service bulletin SEB 99-18 about significant fuel imbalance due to obstruction of fuel tank vent lines. After a protracted engine run and a climb to 5000', this could have further contributed to the problem.

Coming to the ailerons, I don't understand what 'pro-spin' aileron means. An aileron looking down increases the wing's AoA; one looking up decreases it. That's why in normal flight the wing with its aileron down goes up. In a stall, increasing the AoA usually decreases the lift. Well, aileron movement changes the aerofoil shape, thus possibly changing the wing's critical AoA, so this reasoning is not clear cut, but it is still a plausible explanation. So out-of-spin aileron (trying to bank out of spin) causes the lower wing to stall even further, thus acting 'pro-spin', while in-spin aileron acts contra-spin.

Besides, in-spin aileron creates out-of-spin adverse yaw, which again counteracts the spinning. Not really adverse in this case, is it.

In fact, in-spin aileron together with the usual out-of-spin rudder and 'stick forward' is part of the standard POH spin recovery procedure on the Extra with its symmetric aerofoil.

So regardless of what is meant by pro-spin aileron, Pilot X at some point during his recovery was holding full aileron in the correct direction to help him unstall the lower wing.

As for the third question, even the non-aerobatic modifications of the 152 are cleared for spins, unlike the 172. I think 5000 ft is about right as the minimum safe height: it can take up to 3000 ft to enter and recover from a 4-turn spin, and the rule is to complete recovery above 2000 ft.

Now, what I'd really like to know is: which wing was heavier?
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By pplmeir
#1350462
C152 is only approved for spins in utility category, i.e w&B was outside this category
By SimonM
#1430733
1.According to the POH PilotX used the wrong recovery technique for a C152.
He should have followed this (from the POH)...
    1) Verify that the ailerons are neutral and throttle is in idle position.
    2) Apply and hold full rudder opposite to the direction of rotation.
    3) Just AFTER the rudder reaches the stop. Move the control column BRISKLY forward far enugh to break the stall. Full down elevator may be required at aft centre of gravity loadings to assure optimum recoveries
    4) HOLD these control inputs until rotation stops. Premature relaxation of the control inputs may extend the recovery
    5) as rotation stops, neutralize rudder, and make a smooth recovery from the resulting dive.


3. for a C152.... Recoveries from a spin should be completed by 4000ft agl. 1000ft loss of height should be allowed for each turn while in the spin.
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By kanga
#1431932
"..particularly vicious downpour. In fact, the shower was so sudden that the aircraft had been caught at the pumps, with the pilot still refuelling.."

.. with cap still off one of the tanks ?

I wonder if that one tank had taken a significant amount of water during the downpour, but there had not been enough time for it to settle down to the drain sample point, so not apparent during the later check. Then, at 5000', it had, and formed a lump of ice. Then that lump of ice had blocked, possibly partially, the outlet to the pipe leading to the engine. leading to excessive fuel use from the other wing's tank, leading to lateral imbalance ..

Or even, maybe the cap had not been replaced (or not properly, and it was lost in flight), and that had led to imbalance when extreme manoeuvres had started and fuel had been lost from the open filler hole.
By mistral1
#1456004
So what is the correct answer to this then? As a someone who has gained an EASA aerobatic licence, (in a 152) I thought I knew how to get out of a a spin either using PARE or by releasing the controls altogether and pulling the throttle, but this story indicates that there is a situation where this will not work, so it would be great to know before I "discover it" myself.
My theory BTW is due to the cross tank venting design most of the fuel can be taken from one tank before the other, so there may have been a imbalance which wouldn't have helped, but then he did not hold the recommended recovery position (opposite rudder and stick forward) for long enough.
Would like to know the real answer though