Reason for accident - can any one help

[George Tower]

Hi there

I hope you can help me find what caused me to do a forced landing a few days ago in a light aircraft. The incident took place at Upington (FAUP) in South Africa. The elevation of the field is 2791 feet. At the time of take off the temp was 38 degrees Centigrade wind was light and variable.

The aircraft was a Cessna 172 Hawk XP (195 hp 6 cylinder fuel injected engine) there were two people on board and 52 US gallons of fuel. We were well within the weight limit and the aeroplane was correctly loaded.

During engine run ups everything was normal and the mixture was leaned for peak power given the density altitude (6,500+feet). We were cleared to take off on rwy 01 (2438m long). Take off run was fine, rotation normal, climbed away at approx 80Kts until we were about 700 feet AGL, when the airspeed and the rate of climb both dropped.

There were plenty of thermals around so the updraughts and and down-draughts certainly had an effect on the rate of climb. 3-4 miles north of the rwy there is some high ground, so I commenced a very gradual turn to the left - certainly nowhere near as steep as a normal climing turn. During the turn the air was stable enough to maintain a good airspeed and good rate of climb so I contuned the turn on to our track which was about 150 degrees to the left of the rwy heading.

It was at this point that things began to go wrong. Shortly after completing the turn we began losing height at about 300fpm. The airspeed dropped to below 70kts. I was faced with a dilema of pointing it towards the ground and hoping that we would recover enough airspeed. We didn't. The rate of descent increased.

It was at this point that I thought that the best option was to carry out a forced landing - we had mostly flat ground below. Upington town was on our track if we managed to carry on for another two miles and we were 500feetAGL.

There were also power line which were ahead so I had to either pray that we would clear them or make a sharp turn close to the ground - i chose the latter as the terrain either side was flat and free from obstructions. 20 seconds or so from the possibility of a forced landing entering my head we were on the ground. Not a scratch on myself and my passenger. The aircraft had a slight crack in one of the spats on the main undercarriage.

Since then the aircraft was towed to a nearby road, and the engine run. All the indications were normal. The aircraft has since been flown back to Cape Town and there it is having it's MPI.

So to conclude my apologies for being long winded - just trying not to exclude anything. Does anyone possibly know what went wrong and why?

Many thanks for your help.

[RatherBeFlying]

As one PPRuNer signs off, after you make a good landing you can use the airplane again.

While the local pilot community may well have other insights, I can think of two possibilities:
Carburetor Icing: You would need to know the temperature and dewpoint, especially at altitude and check that against the chart
Non-Standard Temperature Drop: There may well have been a substantial drop in temperature in the first few hundred feet such that you needed a richer mixture to avoid detonation. A mild detonation condition would have cost substantial power loss. If you have overleaned a bit, you will see a rise in oil temperature
Somehow I doubt that in the excitement you had a look at the OAT or oil temperature -- don't know if I would remember that either when making a good forced landing is the top priority and there is precious little time to spare problem solving:eek:

[George Tower]

RBF

Thanks for your reply. The a/c has a fuel injected engine therefore carb ice can be ruled out. Your second point however really does interest me - that may explain the crap performance of what I consider to be a very nice aeroplane to fly.

[RatherBeFlying]

Missed that fuel injected part -- gotta pay more attention:rolleyes:

[BlueEagle]

Have you considered the possibility of a temperature inversion?

It is possible that at around 700' agl you entered or passed through an inversion so that the outside air temperature would now be increasing up trough 40C+, possibly to a point outside the performance capability of your engine?

Talk to some engineers in your area as well as experienced pilots, they will almost certainly have some thoughts for you to consider.

Well done with the forced landing!:)

[OzExpat]

Windshear?

Well done anyway! http://www.pprune.org/ubb/icons/icon14.gif

[Captain Stable]

My suspicion is also a temperature inversion combined with over-leaning.

Do you have a METAR and TAF for the relevant time? If so, please post.

Whatever the conditions, if you suspect engine loss of power you should always go to fully rich immediately.

Well done on a successful forced landing. :)

[cwatters]

You don't really tell us what the engine was doing all this time. Were you really at full power and still descending at 300 fpm?

I don't know the field but you imply high ground upwind of the field. Presumably this means there was a down draught off the slope? Curl over?

[George Tower]

I happened to be in the tower just before I took off and their indication was 36 degrees. I think that on the rwy the temp was more like 40 degrees or more and that combined with 2800 feet gives a density altitude approaching 7000 feet.

Wind was light and variable and CAVOK conditions prevailed.

[Genghis the Engineer]

I suspect possibly vapour locking, particularly (but not necessarily only) if you were running on unleaded fuel. You had a hot-soaked aeroplane at a low ambient pressure. This can lead to localised vapourisation of fuel in the lines which can restrict fuel flow leading to loss of power or in extremis a complete engine failure.

I thought you handled it pretty well by the way, an engine failure and cracked spat doesn't even comprise a legally reportable accident.

G

[George Tower]

Indications for manifold pressure, rpm, EGT, CHT, oil temp, oil pressure, fuel flow all normal.

[Flash2001]

Just a suggestion.

Was the engine borescoped for detonation afterward ?

Good work anyway!

After an excellent landing you can use the airplane again!

[BOAC]

2 more 'thoughts' into the pile-

1) I'm with 'cwatters' here - you mention 'high ground' in the take-off direction - standing wave can cause extreme downdraught downwind of such. I think you turned into a wave.

2) If 'lots' of thermals, were there 'lots' of active clouds? Downrush of air from an active cell can ground even a modern jet.

I'm not on the 'over-leaning' nor other engine problem conviction since that would have reduced manifold and rpm, no?

I go for 'weather related' cause/causes

[willbav8r]

Whatever the reason; you kept a cool head, landed yourself and your passenger without injury, minimised damage to the airframe (and presumably anything on the ground).

Whatever caused the incident is separate from the good job you did dealing with the situation.

"You can be my wingman anytime" :D

[Rumbo de Pista]

Lots of theorising here, without much thought about how to proceed with 'investigating'.

First, are you able to involve the state accident investigators? Often, they can be persuaded to examine a minor incident which seems unexplained and offers the opportunity to learn a good lesson before the same set of factors claim a life... I would have thought that if your licensing authority or insurer gets wind of your experience, they might want to look into it, and this would be a good way to do so.

Second, what about other aircraft which took off before or after you? Were there any? Have you spoken to the pilots? Were the ATCOs in the tower surprised at your prompt return to terra firma or have they seen aircraft in similar difficulty before, and if so, in what sort of meterological conditions? How about nearby airfields/gliding sites/whatever?

Third, and it is not normal to reach conclusions early on in an investigation, but have you considered talking to a local university meteorological professor or similar? It might be interesting to provide a set of met. charts, METARs and TAFs, which taken with knowledge of the topography, could lead to some thought as to whether significant standing waves might have been present. There may even be a facility somewhere that is able to 'model' the circumstances and give you some answers.

Fourth, and finally for the moment, what does your passenger recollect - is he/she a regular light aircraft passenger? Ask someone neutral to talk to him/her if you feel it might be of use.

Best of luck with resolving the question! Without professional help, it may be very hard, so I really would suggest pursuing my first suggestion.

[4T winks]

I might just be able to help with this one, I saw an almost identical incident a few years ago in the lowveld, in which a 172 xp had the same symptoms, excepting that the Instructor and Student were able to return to the airfield after a quick but interesting circuit, on landing they tried a run up and found nothing wrong, so rather than take a risk, they called the flight school to say AOG, come fix. The following day we went to collect the A/C, we swapped the fuel divider on the engine and ran it it, all seeemed OK so we did a quick but very interesting test flight around the circuit, problem was still there.

After scratching heads and checking the engine, we had a look again into the cockpit to see if anything had been missed, what we found was a small unmarked knob similar to a vent air actuator, to the right of the mag switch, it was pulled about one third out from the dash, as this was the only thing sticking out, we pushed it in and tried again, hey presto, problem fixed, turns out to be a fuel cut off switch..:eek:

can't rememeber if it was a standard fitting, but the aircraft in question was ZS-JXA

[FWA NATCA]

I echo Rumbo's suggestion to seek professional help from the local Flight Standards people or try discussing the situation with the Cessna Factory Tech Rep who you will find to be an excellant source.

The important thing is to prevent a future accident, and your experience may help educate other pilots not just locally but world wide to a potential problem.

And GREAT JOB recovering from a sticky situation!

Mike

FWA

[calypso]

Well Done! while flying around Nevada last year we arrived at St John three days after a similar incident that ended in tragedy. A 172 taking off from a high and hot airfield stalled and crashed just after TO. Sadly both occupants where Killed. It certainly concentrated our minds getting out of there.

One more thought will be a wind gradient as you lost altitude and airspeed as you turned.

[Tree]

Try looking up the exhaust pipe with a flashlight or push a wooden probe up there to check for blockage.

The diffuser baffles (cones) inside the muff can break off due to fatigue/heat and block the top of the exhaust pipe. The result is a smooth running and normal sounding engine with a very reduced power output. This type of blockage can be intermittent as the lose pieces move around and may not happen on every flight.

It is a known but somewhat rare problem on G/A aircraft.

Also check the fuel tank vents are not blocked and check the mixture control cable for condition and attachment at both ends. Ensure that the mixture control arm on the engine can not move on its own (free-play) due to wear or damage or disconnection.

[Moneyshot]

Sounds like you didn't have much in your favour and I'd put it down to lack of power due to a high density altitude.
I was involved in an accident whilst towing a glider some time ago. Shortly after take off, we started to descend at 700fpm very close to the ground. The glider released and crash landed (no-one hurt) while I climbed away.
The problem was deemed to be related to a down-draught from thermal activity COMBINED WITH standing wave from a mountain range many miles to the North. Although my incident was not density altitude related, the aircraft, a Chipmunk, is not really powerful enough for this role in these conditions.
I suspect, in your case, the very high density altitude combined with the turn and perhaps a down-draught, was enough to cause serious problems. Throw in other factors like engine not performing to spec etc. and you're in trouble. Hope this helps.
Glad you made it.

[Sheep Guts]

Moneyshot I think your on the money!hahah, ok not a great I know

Goerge Tower,
Ok , Ive got my Jeppesen out.

Now you dont give a current QNH for the field, so I will use the elevation 2,800 FEET you say and also 38 DegC. On the CR-5 the answer comes out to around 6500 feet Density Altitude. Ofcourse you could use the formula. Which from memory +/- 120 ft per degree difference from ISA at that PH. You can do the math on that one.

You said all your indications were correct ie. MAP,RPM TEMPS etc. Well were they the normal for that Airfield? Because at 2800feet you wouldnt get the normal MAP as at sealevel. Was the take -off run normal? It would have been much longer than at sea level.

Also you may want to look at your POH, regarding Take Off/Climb Performance with the stated Density height or pressure altitude and OAT, You stated. I dont have a Cessna Manual here but I guess your take off roll would have seemed alot longer than at say Cape Town and also you may not have had the correct Climb speed pegged on your ASI. Just a thought.

Remmember your optimum climb speed varies with and increase in altitude. I know this from doing alot of meat bombing in C-182s. Allways trying to squeeze out the last 2000Ft to 10,000, with 2 Tandems and a Camera. Also in your POH.


Mere suggestions.

You did a good emergency landing Well done!
Your passengers must be very thankfull. I would be, if in their shoes.

Regards
Sheep;) :)

[Lu Zuckerman]

I have no knowledge of the fuel injection system on your airplane and not being a pilot I can’t comment on what was going on around your airplane.

I remember a long time ago in flight engineers school we had it drummed into us that on a multi engine aircraft that lost power on one engine you would place that engine in full rich. A pressure density carburetor has an aneroid metering valve that compensates for density altitude. Does your fuel injection system have an aneroid sensing device. In the large round engine it was a failed aneroid that would not compensate for density altitude reducing fuel flow and, it might be the same on your engine..

:cool:

[heydn]

I must concur with the idea of downdrafts.

I have been in a PA28 where downdrafts have exceeded its performance and curl over from a mountain has exceeded its control capabilities in roll.

Can be a shock and we had 3000' to play with but we lost a 1000' sorting it out.

Well done on the landing

[GARDENER]

I am possibly way off the mark here but... you state high ground to the North-Taking off in a northerly direction could you have been caught up in downwash from the high ground. Been out of school for a while and cannot remember the relevant met terminology but remember the instructor mentioning the "chinooks" in the rockies (extreme conditions).

[MaddogsTwo]

Have you considered standing wave activity from those hills you speak about (lenticular cloud formation?) or were there any CB s within a few miles of the airfield (windshear?)

[flyboy2]

I like the temperature Inversion theory but accompanied by a downdraught/wave/ power-loss

When flying in FAUP at 40 C one has to be extremely careful -you did well to land safely !