The private pilot departed for a long cross-country flight with the mixture leaned to the high field elevation. He then further leaned the mixture for lean-of-peak exhaust gas temperature as he climbed the Cessna 172 to 10,500′ mean sea level (msl) for improved fuel efficiency.
Thirty minutes into the flight, he descended to about 8,000′ msl. He did not enrich the mixture during the approximate 2,500′ descent. Shortly after, the engine sputtered, followed by a loss of about 700 rpm.
He verified the position of the throttle and enriched the fuel/air mixture with one full rotation of the control knob, but he never advanced the knob to the “full rich” position.
He decided to perform a precautionary landing because he was concerned the airplane would not have the power to cross an approaching mountain range. He chose a dry river bed near Tonopah, Nevada, despite the availability of two nearby airports with dirt runways.
During the landing, the plane nosed over and came to rest inverted, which resulted in substantial damage to the rudder.
Post-accident examination of the airframe and engine did not reveal any evidence of preimpact mechanical anomalies that would have precluded normal operation, and the engine achieved full and continuous power during a test run.
The Pilot’s Operating Handbook (POH) required a mixture adjustment during the descent for smooth operation, which the pilot did not do during the 2,500′ descent. An engine manufacturer representative reported that the engine may suffer leaning misfires if the fuel/air mixture is not enriched during a descent.
It is likely the engine sputtered and lost partial power due to the pilot’s failure to properly enrich the fuel/air mixture during the descent in accordance with the POH. The pilot could have remediated this condition if he had advanced the mixture to the “full rich” position in accordance with the POH emergency procedures, however, he instead made a minor mixture adjustment, which did not restore engine power.
Probable cause: The pilot’s failure to enrich the mixture during the descent, as required by the Pilot’s Operating Handbook (POH), and his subsequent failure to follow the POH emergency procedures, which resulted in an excessively lean fuel/air mixture and subsequent loss of rpm. Contributing to the accident was the pilot’s improper decision to land on unsuitable terrain despite the availability of two nearby airports.
NTSB Identification: WPR18LA002
This October 2017 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
I landed a Beech P 58 Baron at WY11 years ago . For those who do not know the airport elevation is about 8,080 feet estimated. The south end is several hundred feet higher.
The P 58 Baron uses Continental fuel injection that is not altitude compensated.
In order to do a go-around the engines mu.st be at full rich. So the approach is made with the mixture richer than cruise at altitude.
On landing in the summer the density altitude is above 10,000 feet.
On roll-out half way up the hill both engines quit cold.
Plane was stopped with the brakes BEFORE it began to roll backward. Started OK and set mixtures to 1/2 travel.
Without the turbos boosting the engines drowned.
Some airplanes, including the Baron 56TC [test bed for Duke engines] and the Duke use a Bendix fuel injection altitude compensated fuel system. Of course I had been flying the Duke and the turbine King Airs which are altitude compensated.
I do not recall a warning in the Beech P58 or 58TC about high altitude landings.
But I remember it now.
When all else fails, read the POH. In fact, it is a real good idea to read the POH BEFORE all else fails. Different engines don’t react the same way. In a 150, you don’t really need to lean the mixture for taxi at a sea level airport. In a 152, you need to or you will foul plugs. Same airframe, different engine.
One difficulty I see is that most of the flight students nowadays have never owned a car with a carburetor, and they have no real idea of how it works or sometimes what it even does. Their cars are all EFI, no mixture control, no choke or primer, no carb heat, they just run. Yes, we really ought to have single lever control, it isn’t 1940 any more. In the meantime, it is up to US to teach them the arcane mysteries of engine management.
For engine longevity / spark plugs fouling/ valve carbon build up etc. etc., you should ALWAYS lean after engine start. No damage can be done at 1000 rpm and no power output but keeping carbon build up off the valve seats is actually a critical component to engine longevity. Upon takeoff you add mixture to the appropriate amount needed for the elevation and DA. And with a fixed pitch prop like someone previously stated above – well you can tell by sound and feel if you have it right – right!?
As all of the literature has stated time and time again- if you are below 60% power it’s basically irrelevant where you put the mixture knob from a peak pressure wave and damage perspective in the combustion chamber.
If you had an air full mixture ratio monitor probe (lambda) it would be obvious and it takes all of the discussion and guess work away from this. There is only one best power “Air to Fuel” ratio (AFR) number for a gasoline mixture. Anecdotally you use EGT’s and fuel flow numbers out of the POH.
So if you were LOP at 10K and descend without adding some gas back into the combustion equation, things could get get quiet in the engine compartment depending on how well the engine actually runs on LOP side of the power curve. If the throttle is way back on descent the pilot might not take notice – and upon the throttle position advancing, it will become self evident with advancing EGT’s and possibly an engine that simply won’t run.
Methinks GBigs has never flown out of a high density altitude airport. This only applies to naturally aspirated engines, not turbocharged engines, but failure to properly lean for take off from a high DA airport will seriously compromise the power available for take off. In extreme situations, failure to lean for taxi may keep the engine from running at all.
This is an example, probably at the extreme level. I departed Leadville (elev. 9984’) on a warm September afternoon 9 years ago in my P172D with a 180hp Lycoming. DA according to the AWOS was 12,100’. As soon as the engine started, I had to lean it a whole bunch just to keep it running. During the runup, I leaned so much for best power that the mixture control was almost at cut-off.
Had I not leaned that day, I could not have taken off. Incidentally, I instructed out of Laramie back in the 70s and 80s—that’s where I learned how to properly lean for takeoff from high DA airports. The DA there in the summer often exceeds 10,000’.
Hard to believe that an aircraft engine not known for it’s ability to run well lean of peak would react like that after only a 2500’ descent. There has to be more to the story.
Also, given that Tonopah is 5430’ MSL, mixture rich for landing is the wrong answer.
This entire article is laughably wrong. There is no reason to lean on the ground or especially lean on takeoff (no matter what the airport altitude is). There is no reason to do a lean climb either, in fact it’s silly because you end up with less power and take longer to reach cruise, burning almost the same or even more fuel. And finally, if descending to land you can still be lean, but if you want the engine to run smoothly on descent you should be adjusting the mixture as you descend in any case…there is no “must have full mixture on landing” rule or necessity. The full mixture landing is usually required if you are doing an instrument approach and may need to “go missed” and therefore want to be closer to your takeoff configuration (note, you are full rich on takeoff.)
Cessna added a leaning procedure to the POH for taxi with the C172R model. Above 3000ft pressure altitude for takeoffs and climbs, the C172 POH procedure is to lean for maximum rpm to maintain optimum power. Not leaning would result in a too-rich mixture and loss of power to some degree.
“There is no reason to lean on the ground or especially lean on takeoff (no matter what the airport altitude is).”
Huh? Try not leaning my AA5-B for takeoff at high density altitudes or elevations – the runway length won’t matter, because you’re simply not going to get airborne. Period. Might as well take the highway.
Or maybe I misunderstood your comment.
fwiw,
mr. little g big is the reason why i rarely read the comment section any more. obviously he hasn’t taken off from a high altitude airport for quite some time. aviation is based 100% upon attitude.
There is one reason, at least one as there may be others, to lean on the ground. I do it to keep the plugs from fouling on our Cessna 182, however, I never depart the runway with a leaned out engine. This is part of my final check off, to make sure the mixture is full rich prior to doing the run up and the departure.
Per C182 POH Takeoff Distance Performance Chart – “Prior to takeoff from fields above 5000 feet elevation, the mixture should be leaned to give maximum power in a full throttle, static runup.” Per Time, Fuel, and Distance to Climb Performance Chart – “Mixture leaned above 5000 feet for smooth engine operation and increased power.
The Cessna 182T/G1000 requires leaning for max RPM for taxi. Full rich for takeoff, approach and landing. If you don’t you will foul the plugs.
What kind of aircraft do you fly? I fly several — admittedly all GA, piston — and EVERY ONE of them calls for leaning at higher density altitude and on the ground. Most specifically point out that maximum power output from the engine is achieved by setting mixture at some level LESS than full rich.
Please enlighten us on exactly why it is your comment that isn’t “laughable”, because my experience is that you are either mis-communicating your intention, or horribly misinformed.
Obviously you’ve never done any mountain flying.
I’m not sure if it is more concerning your information is wrong, or how confident you seem to be about this incorrect information.
For those seeing the comment from the guy who didn’t submit his name, I would encourage you to read this from Mike Busch, IA and National Aviation Maintenance Technician of the Year in 2008, also an experienced pilot:
“As soon as the engine starts to warm up (less than a minute after start in temperate weather, perhaps a couple of minutes if it’s really cold), you should lean the engines for taxi. Retard the mixture control until the engine starts to stumble, then enrichen a bit for smooth idle. You cannot hurt the engine by leaning it at these power settings…but you will hurt it if you taxi around with the red knob full forward.”
Gbigs your ignorance never ceases to amaze! The problem is there are too many pilots like you out there who don’t understand how the engine/carburetor works and will take what you say about thefuel injected altitude compensated engine in your $700K Cirrus as true of all engines. Regardless of what the actual circumstances were in the case described here you are TOTALLY WRONG about the need to lean a carburetor or non-altitude compensated fuel injected engine for density altitude. Do a little research before you spout off!
A plethora of great decisions!!
So, the message here?….. Don’t let the Maint. Director fly the airplanes he maintains.!
Also, he has 100 hrs pic and 9 hrs in type…. So, he needs a LOT more instructing on how to correctly use the mixture control.
Then, he crashes on a huge dry lake bed and finds the wet spot with a ditch that flips the aircraft, which is probably now junk, or salvageable for parts.
Yes. Every C172 POH I’ve seen says to lean for maximum rpm for takeoffs and climbs (above 3000′ elevation), so leaning using the EGT was the wrong thing to do in the climb. And in cruise, there’s recommended lean (50 degree rich of peak), or peak EGT for economy lean. But under some conditions peak can cause engine roughness and the mixture should then be put at recommended lean. Lean of peak is not shown as an option.
I don’t think the NTSB is saying full rich is necessarily the optimum mixture setting when the power failure was occurring but saying that if the emergency procedure had been followed, the pilot would have at least restored power and also realized he simply hadn’t enriched the mixture enough.
I always lean aggressively as soon as the engine is warm enough. Leaning after a cold engine start gets the plugs hot enough to not collect lead, which will show up as a fouled plug during the run up.
I also lean during a climb, once above 3,000 msl.for max. rpm, as well as in cruise at any altitude.
As far as richening the mixture. A friend was landing at Casa Grande, NM on a 105 degree day. He went to full rich on downwind and the engine flooded and quit.
The density altitude was 7,000 ft….
It is stunning to me that in this day and age after valid and verified data in lean of peak discussions, POH/OM procedures, engine management seminars, blogs, YouTube videos, sophisticated data from EDM’s, etc. that we are still not on the same page WRT aircraft engine operation.
As a long time CFI, proper engine management is a primary concern and an important item of discussion with students at every level of experience who I encounter.
Until we dumb the fuel/air mixture process down for the masses with a FADEC system, knowing the appropriate use of the red knob is mandatory. After all these years have passed with the red knob’s persistent and ubiquitous presence, what could possibly be the remaining issue with it’s operation?
JimH – Hopefully he would have noticed that somewhere in the middle the power would have been fully restored.
Warren,
Yes, just richen the mixture to get max. rpm. I very simple concept, especially with a fixed pitch prop.
Jim, Actually I meant that to be in reference to the NTSB comments and the accident pilot’s actions. But in reference to your friend’s experience, I suppose he promptly leaned and everything was ok?
Warren,
Nope, He couldn’t get it restarted, and since he was on downwind with little time, he dead-sticked it in, landing ok.
Sounds like he was flying a nice tight pattern….
Dale,
That’s the way the Air Force Aero Clubs teach; a tight pattern and power off 180’s to a landing.
Beale AFB is 113 ft msl., so some get lazy/ forgetful on proper mixture control.