Late Go/No-Go Decision (a lesson from Aviation101)

[Garfly]

 

 

 

 

[skippydiesel]

I empathise with the pilots in this video and congratulate them on their decision not to continue.

 

Recently I made the very wrong decision, to take off into unexpectedly deteriorating weather conditions. My anger at myself for doing so, then led to "downstream" errors of judgement and poor airman-ship - I was lucky not to have or cause an accident. 

 

Pride comes befor a fall and I prided myself in my airman-ship. I now realise any of us can make a silly mistake that may lead to a disastrous conclusion.- - be warned!

 

 

[APenNameAndThatA]

Fantastic video. I wonder if the jiggling ASI is an advantage of steam gauges over glass ones? I thought that they were going to abort the takeoff because of the cloud but that was not it at all. 

 

 

[facthunter]

 They had far more runway than normal., and actually got airborne in ground effect. It really should have been aborted earlier, when it was obvious there was  not a normal speed rise in the usual time. I never saw the rev counter and would suggest the engine wasn't getting full power or it was a hot and high airport. Nev.

 

 

[Garfly]

Big Bear is 6,750' elevation.

 

Here is a video about it:

 

 

 

 

 

[mkennard]

I've never heard of "Wing Up" before. Unnecessary isn't it?

 

 

[w3stie]

They made it out the next day before more weather.

 

 

 

 

 

[poteroo]

Wise decision. Thought they might have anticipated that a weather change moving 'in' from the West would have caused a westerly breeze for a few miles ahead of the actual 'front'.  Perhaps a call to their BoM would have been worthwhile when they arrived.

 

Now - a few comments on their technique for high altitude operations. Airfield altitude was 6750 ft and OAT = 5.  So, this gave them a DA of 6750 + 6 x 130 = 7530.  They wisely kept fuel load to a minimum in view of their performance, but the aircraft would have needed a MTOW of less than the book MTOW because of the climb / weight limitation, (due altitude), in the P charts: they were probably below this, so the aircraft would probably have achieved the book number of 6 degrees AoC had they taken off.

 

However, the Cessna POH states that for higher altitude takeoffs - zero flap is recommended.  They used 10 degrees, which creates sufficient drag to be limiting. This reduced their acceleration,and they noted how slow things were going early on in the roll. 

 

No mention is made of leaning the mixture.  At this altitude, the required fuel flow for wide open throttle would have been 75-80% of full fuel flow at sea-level. Cessna recommend leaning the mixture above 3000ft.  This is easily done by running up to full power, (wide open throttle), on the brakes and then very delicately leaning the mixture to create an RPM increase - but not beyond the peak. If there was a fuel flow readout - it would have probably shown a decrease in flow of around 20%.  Don't try to do this 'on-the-run' as it is very distracting.

 

It appears that they made a 'standing start' take-off whereas the smarter technique would have been to conduct a 'rolling start' using every last metre of runway. This is often worth at least 10kts. 

 

Had they continued with the takeoff, the aircraft should have been accelerated through 59 KIAS to at least 65KIAS before 'rotating'. Even more important with any tailwind component.

 

There's been a lot published about 'hot & high' operations in the USA as they have a lot of their locations above 6000 ft. While HP is part of the answer, good technique can be the finishing touch for safety.

 

happy days,

 

PS: the pic below is of a Mission Cessna 180 landing on Keglsugl, PNG. (8450 amsl) in the late 60s. Only the 7-8% downslope allowed these normally aspirated aircraft to get airborne.

 

 

 

[turboplanner]

Your comments are a good example of where the GA Performance and Operations module training gets your mind off the one size fits all thinking, and the Density Altitude calculation immediately sets you down a path of checking all the high altitude requirements.

 

We don't have as many high altitude fields in Australia, but you don't need 6000' when our hotter temperatures kick in to have a new set of problems to plan around.

 

 

[Thruster88]

Only 32C and 1010mb at Orange will get you 6000', a few have failed to get airborne despite the long runway. 

 

 

[poteroo]

Only 32C and 1010mb at Orange will get you 6000', a few have failed to get airborne despite the long runway

 

Can be very chastening with low HP aircraft. 

 

One point that I forgot to mention in previous post was in regards to tyre inflation on sealed runways.  The higher you keep it - the less drag is suffered.  Learned this when operating normally aspirated C206 off Flagstaff, (Arizona,US), which is 7000' amsl. Had 8.00 tyres with not a lot of inflation in them for use on backblocks strips. Surely hindered our acceleration and could have really hurt if we'd had a crosswind.

 

We should really be placing a lot more emphasis on performance in RAAus - but in 12 hrs of cross-country, there is only so much that can be taught.

 

happy days,

 

 

[aro]

Wise decision. Thought they might have anticipated that a weather change moving 'in' from the West would have caused a westerly breeze for a few miles ahead of the actual 'front'.

...

 

However, the Cessna POH states that for higher altitude takeoffs - zero flap is recommended.  They used 10 degrees, which creates sufficient drag to be limiting. This reduced their acceleration,and they noted how slow things were going early on in the roll. 

 

No mention is made of leaning the mixture.

 

... 

 

Had they continued with the takeoff, the aircraft should have been accelerated through 59 KIAS to at least 65KIAS before 'rotating'. Even more important with any tailwind component.

 

I agree about the weather, it looks like the rain caused a down draft which translated into a strong wind blowing away from the rain, the same direction they took off. This is probably a common danger if you're taking off to beat weather.

 

I gave them the benefit of the doubt on the mixture, they said "mixture set" rather than rich, and it didn't look fully rich.

 

The flap setting is a very important point. I looked up a C172M POH online and definitely flaps 0 would be appropriate, particularly at high altitude.

 

I disagree about the speed though. Waiting for 65 knots to rotate or climbing at 65 knots would degrade performance. For a maximum performance takeoff the POH specifies 

 

• Flaps 0
   
   
  
• Climb speed 68 mph (59 knots) until obstacles are cleared.
   
   
  

 

 

For a flaps 10 takeoff, 65 mph (56 knots) until obstacles are cleared.

 

Flaps 10 gives you a lot of extra drag. Too fast as well gives you extra drag squared.

 

(Obviously that is slow and could be a problem in gusty conditions like this. Gusty winds and a requirement for a maximum performance takeoff might be a good reason to stay on the ground.)

 

Often during training a few extra knots are added for "safety" and comfort. That doesn't usually matter because we usually have performance to spare. However, it can be deadly if you really need that performance.

 

If there is any doubt about takeoff performance, know what configuration gives you the best performance, and know what speeds to fly to get it.

 

However, whatever the reasons for the problem, the abort decision was good. Problems can happen to anyone, and it would be easy to sit there in denial and wait for the aircraft to climb until it is too late. Takeoff accidents are statistically much more deadly than landing accidents.

 

 

[facthunter]

 You can hang there inground effect but try to climb out of it and you have a problem if you have inadequate power. IF you are really critical you may have to clean up the plane while still in ground (or water) effect. You need a safe INDICATED airspeed to climb away which is dependent on your ACTUAL AUW and any gusts likely. You will feel you are going faster than normal in a downwind. Any Turbulence reduces performance, also . In tailwind conditions you have the added problem of the tailwind increasing generally as you climb initially , (windshear) robbing you of the acceleration you would normally hope for. Rain can bring down air currents which will outflow from a central point turning a headwind into a tailwind for you.. If your situation is critical do early  power checks  on brakes or a rolling start , be sure of your load and make decisions early rather that later, particularly on shorter length runways with obstacles  in  the take off path. You don't always have the option of landing on the runway straight ahead. Soft tyres will heat up more than hard ones as well as being  robbers of power. High and hot (high density altitude) takeoffs downwind are more likely to have a tyre failure as you are spending more time at a high (actual) speed with weight on the tyres and you are working  the brakes harder when you have to stop also. I never see birds trying to take off down wind (except when they are very young). You should have a good reason to have to do it. For most it's an abnormal operation and should be treated as such. it's probably not done in training for most people, I fear.  Nev