Carb ice catches Cub

Aircraft: Piper Super Cub. Injuries: None. Location: North Myrtle Beach, S.C. Aircraft damage: Substantial.

What reportedly happened: The pilot was conducting a banner-tow flight. The accident happened as he approached to pick up the banner.

The airplane was at an altitude of 300 feet AGL when he reduced the power to the idle. His said his airspeed was between 60 and 70 mph and he had not activated carburetor heat.

The airplane descended to about 10 feet AGL and was 50 feet from the banner pick up poles. He added full power and noticed that the rpm was at 2,500, which was 100 rpm less than what full power should have been.

He pitched the nose up and the airplane climbed to about 200 feet. The rpm continued to decrease, dropping to 1,500 rpm.

The pilot lowered the nose to maintain airspeed and verified the throttle was full forward. He increased the mixture, and there was no change in rpm. The airplane would not maintain altitude.

The pilot told the tower that he was going down. He reduced the throttle to the idle position and lowered the flaps to the full down position for a forced landing beyond the banner tow grass area. The airplane collided with the airport perimeter fence and nosed over.

A carburetor icing chart indicated that the airplane was at risk of serious icing at glide power given the weather conditions at the time of the accident.

Probable cause: The pilot’s inadequate use of carburetor heat during cruise flight, which resulted in a partial loss of engine

NTSB Identification: ERA12LA453

This July 2012 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.

Comments

  1. says

    Forgetting the carb heat during descend can be very dangerous. That is not the first and probably not the last incident caused by it not being applied.
    During my training i called carb heat – my best friend as had a problem remembering about applying it.

    • Ray says

      I too remember coming into short final after a long approach on a humid day only to look down and observe the carb heat knob kissing the panel, makes the little hairs on your neck stand up! At the begining of our flying we are given a bucket of luck with a hole in it, get things right before it runs out.

    • Greg W says

      The temp. was 73* F so the heat/density altitude should not have been a problem, however. I do not know what that model super cubs instructions are but my PA-22-135 owner handbook states,”lean mixture any time an increase in RPM can be obtained”, we don’t know but perhaps he had gained a few rpm’s by leaning before take off. Carb. ice would have been my thought,with a steady rpm loss after a glide. However it is much more rare to have bad carb icing with Lycoming engines due to the carb. being mounted to the oil sump. The warm carb./intake pipes also lead to a richer average mixture than an equivalent Continental engine. Many Lyc. installation say”check carb heat”, Cont. installations often read,”apply carb heat” that is why.

  2. Pete Schoeninger says

    Lycoming’s don’t get carb ice too often, and many pilots think carb ice is a non issue. NOT SO. Ray is right, carb heat on, always, just before power reduction.

  3. Ray says

    first, whenever you reduce RPM to idle you ALWAYS apply carb heat. (primary training) And what is up with increasing the mixture at 300 feet? Grand strand airport is at sea level so the mixture should have been at full anyway. Tow pilots are commercialy rated………one wonders.

    • Richard says

      I agree with Ray about always apply Carb Heat when you reduce RPM to idle, however, the pilot probably had read this statement from the Piper Super Cub Operators Manual under Approach & Landing: “The carburetor heat need not be used unless icing conditions prevail, but the engine should be cleared occasionally by opening the throttle.” He probably didn’t think icing conditions were as bad as they were.

      • Paul says

        One thing is certain – whether Piper advises such or not, applying carb heat won’t result in the airplane ending up in a heap on the ground but carb ice can and will cause such an end result for carbed engines when the power is pulled off in a descent if the conditions for carb ice exist which obviously requires some preflight attention to that detail. Carb heat can always be reduced or closed if it is deemed to rob the power too much. As soon as the RPM was observed to be abnormal that should have been an automatic trigger to reach for and apply carb heat.

        • Pete Schoeninger says

          Paul is 100% right. Same situation in Cherokees. Piper says use as needed. When the engine conks out from very infrequent but often possible carb ice that’s too late. We always taught our students in Cherokees, Cubs, etc. just use it just before power reduction, and any time the engine seems a little rough, and leave it on for a minute or two, period.

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