Too rich mixture leads to poor performance

Aircraft: Cessna Cardinal. Injuries: None. Location: Rock Springs, Wyo. Aircraft damage: Substantial.

What reportedly happened: The elevation of the airport is 6,764 feet MSL. The density altitude at the time of the accident was calculated to be 7,907 feet.

The pilot leaned the mixture to start the engine, but he did not lean the mixture prior to takeoff.

He did not remember using the Before Takeoff checklist, however, he stated that during the engine runup he observed that both magnetos dropped 50 rpm, and that he cycled the propeller three times, and each time the propeller recovered in a normal time span of between three to five seconds.

The engine was strong and smooth on takeoff and climb, but when the airplane was about 500 feet above ground and in a right turn, the engine began to vibrate and the plane started to lose altitude. The pilot made a forced landing, which collapsed the left landing gear.

The airplane’s owner’s manual notes that, for maximum rate-of-climb performance at airports above 5,000 feet, the mixture control should be leaned.

Probable cause: The pilot’s failure to lean the fuel mixture prior to takeoff, which resulted in the engine’s inability to attain sufficient power due to the rich mixture, and his inadequate preflight planning.

NTSB Identification: WPR11LA463

This September 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it isintended to help pilots learn from the misfortunes of others.

Comments

  1. Curious George says

    Sounds like this was accident was a partial replay of the Bruce Meadows Stinson accident (where the pilot didn’t even know he should lean). That accident report is a very good read (look it up using Stanley ID, and June 2012 at http://www.ntsb.gov. I’m sure most US pilots have seen the excellent in cockpit videos of the short, five minute flight that are posted on YouTube and elsewhere.

  2. Jerry Olson says

    There may be another bear in these woods.

    I own a Cardinal RG, which I have owned and flown in and out of Colorado from my sea level airport for the last 35 years. I just returned from a trip to Colorado this last weekend. On this trip I had two instances where I encountered mixture issues.

    The first was taking off from an en-route fuel stop airport. This airport has a field elevation of 3,800’, and the DA was around 9,000’. During the 1,800 RPM run-up I leaned the engine for max RPM, then enrichened it about ¾ turn. This left the mixture control about ¾” out from full rich. During run-up, the mag drops were on about 50 RPM on both sides, and the engine analyzer showed EGT’s on all cylinders at levels I expected. On takeoff, I lifted off and about 1/3 of the way down the 6,000’ runway, but the plane was not climbing as I expected. The EGT’s appeared normal, but the fuel flow appeared low. Turning on the boost pump made no difference, so I pulled the power and landed to determine if there was some fuel issue. (On a Cardinal RG, with its high wing, the POH does not require the boost pump be on during take-offs.)

    On the subsequent run-up, everything appeared normal. So, I again took off, only this time with a slightly richer mixture. (About ½” leaned from full rich.) This take-off proceeded as expected.

    The second issue was when I took off from the airport in Colorado for the return trip. This airport is at 6,800’ and the DA was about 10,000’. After engine start I leaned the mixture about 1’ for taxi. After a fairly long taxi, the engine died as I pulled the throttle back from about 1,000 RPM to 600 RPM. The restart took a bit due to the engine being flooded. After restart, the run-up was normal and the same as at the 3,800’ airport. For take-off, this time I turned the boost pump on. Take-off was normal for that altitude and DA, with the mixture backed out about 1” from full rich.

    The engine has just over 200 SMOH, and the fuel injection servo was also overhauled at that time. The big difference; I recently replaced the mixture control cable. The vernier control in the old cable had failed, and the cable had slack due to the cable housing cracking. The new mixture cable is much more sensitive.

    I certainly wouldn’t say I couldn’t be getting rusty. But I’m thinking the issues I encountered had more to due with the sensitivity of the new mixture cable than anything else. I’m also suspicious there be an issue with the mechanical fuel pump

  3. Vaughn S. Price says

    I hate to sond like a broken record but this accident was caused by the pilots 1st instructor. he was not taught the simple concept of high altitude takeoffs. which if instructed properly the student would be required to take off with 3/4 power using the complete runway and staying in ground effect until able to climb at normal climb speed

  4. Mooney 9242V says

    Pretty basic stuff, leaning an engine and following a checklist. Think the pilot, with the benefit of hindsight, would be willing to trade a useless third class medical certifictae for an an hour of flight training each year, focussed on emergency procedures?

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