Discuss the problems and solutions to all of the situations that Pilot X finds himself in.
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By G-BLEW
#950100
Hot, Humid and Hasty


Another busy day in the office for Pilot X, but it’s so hot and humid, and the flies get up his nose!
Liam Watt explains


Pilot X was feeling very confident. He’d been flying an average of two hours a day for more than two months and felt that he could handle anything. On this particular morning, he’d been slow to prepare and consequently the gliders were lined up and waiting for him. Pilot X ran over to the glider tug and hurriedly strapped himself in. He felt very conscious that he was holding up the glider pilots who were waiting eagerly in their hot and humid cockpits.

Pilot X was sweating profusely and getting frustrated with the flies that were intent on literally getting up his nose. He was more used to the cool English climate – the close to 40°C with 90% humidity was almost unbearable. He was very keen to get into the sky and cool off in the higher air. The well-used tug fired into life and Pilot X rushed through his pre-take-off checks and lined up for the launch at the same time. As he scanned the sky, he was momentarily distracted by the magnificent towering Cu and building Cb that were all around. The morning briefing had shown that the day was going to be extremely unstable with showers and thunderstorms by early afternoon. While moving forward and taking up the slack in the rope, his mind began to wander. He thought about how the 100-hour check was nearly due and pondered about how much time the degraded exhaust had left. With this in mind, he listened intently to the engine and even thought he could hear a slight change in the engine tone.

Not quite right

As the rope went tight, Pilot X eased the throttle to full and the ageing Lycoming 180 groaned into life. Pilot X was sure that if there was a problem he would be able to spot it during the take-off roll – he furiously scanned the gauges but nothing appeared to be abnormal. Everything was in the green and the manifold pressure was near atmospheric. But still he thought that something was not quite right. A quick glance in the mirror confirmed that the glider did not have his airbrakes open.
While the speed began to build as the aerotow combination trundled down the runway, to Pilot X’s alarm it was about 15kt slower than it usually was at this point. He urged on his ASI, looking for 40kt so he could engage the first stage of flap. The tug bounced over a lump in the runway and sank back onto the ground. Pilot X became acutely aware that he was normally airborne at this stage. At that, he scanned the sky ahead and to his horror saw that the sightline angle to the trees on the horizon looked much flatter than usual. He knew that he would have to make a decision very quickly.
“This is the final straw,” he thought, convinced that something must be wrong. The end of the runway was rapidly approaching and he decided that there should be enough remaining runway for the glider to land on. Besides, the luxury of enough runway was soon to run out and he would rather end the glider’s flight here, at the end of the runway, than risk heading off over the trees. That was, of course, if they could even get above the trees. Without another moment of thought, Pilot X yanked the glider emergency release cable.

With a jolt, the tug accelerated and climbed into the air. In what felt like slow motion for Pilot X, his hand went for the throttle and he rapidly drew off the power. As the nose lowered and he looked at the runway ahead, he felt a mild sense of panic. The amount of runway left for a landing looked very marginal, but he pressed on anyway, convinced that something was wrong and he should get the tug on the ground. Pilot X touched down and applied maximum braking, which simply did not feel enough, but he knew that any more braking would probably result in a nose-over and would certainly damage this taildragger. With the aircraft racing towards the bushes, he applied maximum flap in the hope that the extra drag would stop him in time. Pilot X felt he could do no more.

The end of the runway came and went as the poor tug ploughed over a taxiway and into scrub. Higher bushes were approaching rapidly and Pilot X fearfully applied even more wheel braking. With that the tug finally skidded to a stop in a cloud of dust. Pilot X, still feeling a sense of panic, magneto cut the engine and switched everything to the off position.

Nothing broken

As the dust settled, he undid his straps and rolled out of the aircraft, feeling a little shocked. Astonishingly, only the nose cone of the tug was in the high shrubland and nothing was broken. Pilot X walked around to the back of the aircraft and suddenly remembered the glider that he had just ditched. Looking back at the runway he saw to his relief that the glider had landed on the runway and appeared to be OK. After the tug had pulled the release there’d been a pregnant pause as the poor pupil took in what had just happened – then the instructor took over and safely landed the glider off to the right of the tug.
Pilot X was still looking at the glider when he saw the canopy fly open and the Chief Flying Instructor come charging out…

Questions
1 According to cockpit resource management (CRM) thinking, what dangerous attitudes did Pilot X display and what were the possible remedies?
2 What two central factors conspired to
cause a marked change to the aircraft’s performance?
3 What third factor was present during the launch that affected the take-off – and why didn’t Pilot X notice it?
User avatar
By CaptCrispy
#950326
Keep in mind I am a fairly new (almost) pilot and have no knowledge of gliding, but I think there are several 'common' problems that can seen.

1) The main problem was probably rushing almost everything from approaching the tug to take off, there was lack of concenration and the stress of delaying others as well as being uncomfortable (hot, flies, etc). I imagine the best solution would have been to slow down, maybe give up the slot and go through things properly.
2) I expect the main impact on performance was the hot and humid air, both consipring against performance and possibly forming carb ice, and applying carb heat may have been missed on the rushed check list
3) Not sure about this, perhaps the storm that was forming affecting the pressure, wind speed/direction, microburts, etc?
User avatar
By dont overfill
#950384
I think CaptCrispy has some of the answers - but-

1) Familiarity was making him complacent. Should he have flown knowing there was a problem with the exhaust? Lack of time was putting him under pressure hence little self briefing or pre flight checks.
In the rush to get airborne did he do performance calculations for the conditions on that day. The flies that were getting up his nose may have been squashed on the prop and wing leading edge from the previous day degrading the performance of an already tired aircraft. Were they perhaps also in the pitot or static? Perhaps a soft tyre? Did he do a static RPM check knowing the exhaust problem?

2) The high temperature and humidity were without doubt major factors in degrading the performance. Not enough info on the change of engine note. It could have just been caused by the humid conditions or was it the exhaust starting to collapse internally?

3) The nearby thunderstorms could cause a rapid change of wind direction resulting in a downwind takeoff. The assumtion that a glider lined up ready to go was pointing the correct way was his "mental wind sock."

D.O.
User avatar
By CaptCrispy
#950434
Agreed, all good extra notes D.O.

Not forgetting Pilot X did almost 2 hours a day for 2 months, so possibly also tired. Feeling something was not right plus the engine tone should have caused him/her to abandon immediately.

Apart from a bruised ego and angry gliders at least by stopping before leaving the ground you have safe options; you could think about things for a few minutes, maybe over a cuppa to calm down. You would then have time to think about things properly (performance, weather, implications, etc) and you could then take your time to redo check lists (inside and out) properly which would help to identify any major issues.
User avatar
By Lowtimer
#950800
Agree with DO: I think he most likely picked up a tailwind due to changes in local winds associated with the strong thermal systems going off all around.
By Dave182
#952469
It was hot and humid but it does not say how high. Could a lack of engine leaning to get peak performance also be an issue?
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By CaptCrispy
#952488
Dave182 wrote:It was hot and humid but it does not say how high. Could a lack of engine leaning to get peak performance also be an issue?

I don't think so, but as I said above I am not an expert and I am sure (in fact I hope) the experts will correct the following if it is wrong.

Leaning is based on altitude because of the less dense air and the recommeded altitude for leaning is (usually?) stated in the POH. So leaning is done on reaching a certain altitude in the cruise and any time after that the altitude changes.

However, I believe it is acceptable to lean at any altitude to adjust for density BUT not if the engine is at more than a certain percentage of power (75%?).

As Pilot X was on the take off run I presume he/she should have been at full power
By johnm
#954256
If the density altitude is high you may well need to lean quite agressively to get full power for take off. Quite common in poarts of the USA.
User avatar
By Capt Edmund
#955049
At 40 Deg C he'd be above ISA so you'd expect acceleration to be reduced and IAS to be less that TAS. As said above, the exhaust is an issue as failure would have an impact on engine power but wouldn't, I think, have made much of a difference to the gauges, or at least not within the time it takes to get off the ground although RPM would have been lower than normal.

The actual glider being towed would make quite a difference to the performance too, which would best be considered by the pilot when thinking about departure. A 2 seat glider will be heavier than a single, a student pilot will probably not be as stable as an experienced one which would caus extra drag. You'd also be wanting to consider the implications of having a trailer on the contingency plans. If you've not got sufficient airspeed by a point you can either both land-ahead or cast off the glider to land which would reduce the drag on the tug and, if given sufficient distance, allow acceleration to safe flying speed.

I should point out that I have no experience of aerotows so I don't know if that is a huge no-no or what your SOPs would be. The though of having 2 ac rejecting a takeoff at the same time is disturbing, especially if you are counting on the glider pilot to spot what's going on and make sure they miss the tug!
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By mo0g
#956315
CaptCrispy wrote:
Dave182 wrote:Leaning is based on altitude because of the less dense air and the recommeded altitude for leaning is (usually?) stated in the POH. So leaning is done on reaching a certain altitude in the cruise and any time after that the altitude changes.


Air density is also directly affected by temperature, not just air pressure. You are meant to calculate "density altitude" based on pressure/temp, then check landing/take-off distances at that density altitude. The hot/humid weather would have increased the take-off roll required, which is evidenced by him running out of runway.

Also, if the engine wasn't leaned and it needed it, his engine would not have been performing to its max, and exacerbating the take off distance problem. As would any tailwind obviously.

Complacency, weather, lack of pre-flight planning and environmental conditions all contributed to the problem. I would also suggest the mention of known problems with the aircraft, and waiting to put them right would indicate the lack of a proper maintenance regime and therefore other more serious problems with the aircraft could have been developing unnoticed.
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By CaptCrispy
#956330
Thanks mo0g, I understand about the temperature but still don't understand leaning in the take off run.

As I said I'm no expert and I can't remember the details; but I am sure I read something in aircraft technical about leaning above a certain power (around 75%) has negative results, again I can't remember what negative results.

I always assumed the take off run is at full power (without red lining) and therefore you could not (or it is not advisable) to lean during the take off.

Keeping in mind my inexperience, I suppose the question should be is it possible (or advisable) to take off at less than full power?
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By mo0g
#956469
Im sure there is something in a manual somewhere which talks about the engine running rough, or not generating full power, so you may need to lean the mixture.

If you think about it though, power is generated from combustion in the engine. Combustion is a function of the fuel/air mixture, and if that mixture is too rich or too lean it wont generate the optimum power.

I just did a quick google and found this sentence..
"Additionally, at power settings of less than 75%, or at density altitudes above 5,000 feet, it is essential that normally aspirated engines be leaned for maximum power on takeoff unless equipped with an automatic altitude mixture control."

And I found this in a lycoming engine operation pdf
"The normally aspirated engine performs and reacts to density altitude. As an example, his type powerplant at takeoff from an airport with an indicated altitude of 3,000 feet, but with an ambient temperature at 85oF, would have a density altitude of more than 5,000 feet. The engine would lack some 20 to 25% of its power and also probably run rough because of a rich mixture on the ground at full rich. Therefore, the typical normally aspirated direct drive engine requires the mixture be leaned on the ground for efficient takeoff performance where airports are 5,000 feet (density altitude) or higher. The overrich condition is something the pilot can compensate for by leaning. However, the higher density altitude with its thinner air cannot be compensated for with a normally aspirated engine unless a supercharger or turbocharger unit is added to the powerplant. Thus, at density altitudes of 5,000 - 6,000 feet, the pilot of a normally aspirated engine has available to him approximately 75% of the engine power, and must plan his takeoff accordingly after setting the mixture."
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By mo0g
#956471
And I just noticed that the article is telling us he is NOT in the UK "..he was used to the English climate", so this confirms the possibility that he is operating from a new high altitude airfield and due to the other factors has not thought about density altitude at all, which is exascerbated by the hot humid weather.