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10 Answers

Airspeed Not Registering: Abort Or Go-around?

Asked by: 6714 views , , ,
Aerodynamics

Studying for a CFI checkride, this NTSB accident report bubbled up:

* * * * * * * (begin)

NTSB Identification: NYC00FA001. 
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division 
Accident occurred Saturday, October 02, 1999 in CALDWELL, NJ
Probable Cause Approval Date: 03/02/2001
Aircraft: Cessna 401B, registration: N88VA
Injuries: 3 Serious,5 Minor.

The pilot aborted the takeoff run after the airspeed indication rose to about 80 miles per hour, but would not go any higher. He could not stop the airplane, before it went off the end of the runway, over a berm, and into a drainage ravine. When the airplane was pulled out of the ravine, both pitot covers were still in place, around the pitot tubes. The runway was 4,553 feet long, calculated takeoff distance was about 2,525 feet, and calculated accelerate-stop distance was approximately 2,950 feet. Tire skid marks started around 3,600 feet from the approach end of the runway, and led to the wreckage. About a year earlier, another airplane was destroyed when it ran into the same ravine, which was located about 200 feet from the end of the runway.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

The pilot's inadequate preflight, which resulted in an attempted takeoff with the pitot covers installed. An additional cause was the pilot's delayed decision to abort the takeoff, while factors included the misleading airspeed indications, and the proximity of the drainage ravine to the end of the runway.

* * * * * * * (end)

Here's the question: "hindsight is 20/20," but should the pilot have opted for a normal takeoff, and immediately returned for a normal landing? My experience with small planes would say yes, partially because on Cessnas the pitot tube is visible from the cabin. But what about low-wing a/c? What about bigger a/c? If you butt tells you everything is normal about airspeed and takeoff -- i can't believe the airplane felt like it was only going 80 kts at takeoff power halfway down the runway -- but the ASI isn't normal, abort or go-around? 

Thanks, guys.


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10 Answers



  1. tekkie79 on Sep 01, 2012

    Abort, abort, abort.

    The runway is long enough that he should have noticed the issue before the half way mark.

    Moreover, the speed indicator will likely have read 80mph during taxi which would have been another indicator.

    Finally, without a speed indicator making a proper landing (flaps or no) is a dangerous proposition and considered an emergency situation. By forcing a takeoff, you are purposefully creating an emergency situation which no pilot should ever do.

    However, if the aircraft was in a normal takeoff configuration and the pilot was not forcing the stick forward (very bad), the plane would have lifted naturally. Another indication.

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  2. Nathan Parker on Sep 01, 2012

    “should the pilot have opted for a normal takeoff, and immediately returned for a normal landing? ”

    If there isn’t room to stop safely, then probably so. Anyone should be able to safely fly a light airplane with no airspeed indications. Most pilots probably already know the proper pitch attitude and power setting on final, they just need to realize they know.

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  3. Wes Beard on Sep 01, 2012

    I once found myself in both positions. A bug was caught in my pitot system. I was taking off in a C172 and I looked over to verify my airspeed which was zero. I was probably going 60kts when I decided to abort. I had no question it was a good decision. A cloud layer at 500 ft AGL would make the situation far worse. I had enough runway to stop but applied considerable braking action.

    Earlier in my studies a piece of tape was left over the cover of the pitot shaft after it was washed. It was clear and I didn’t think to examine it closer. I had just rotated in a PA28-161 when I saw the airspeed zero with not enough runway to land and stop. I made a shallow climb knowing I was faster than VY due to full power and low pitch attitude and circled around and landed.

    I don’t think there is enough information in the part of the report you listed to make a determination of the pilot decided on the best option. It is possible he made the best option but the outcome was still bad. I think the report stresses the importance of preflights.

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  4. John D. Collins on Sep 01, 2012

    If you do a takeoff performance calculation, you will obtain the approximate runway distance to takeoff. Assuming a normal constant acceleration, you will reach approximately 70% of your takeoff speed at half the distance. In my Bonanza, my takeoff speed is 71 Kts. 70% of 71 Kts is approximately 50 Kts and I use this as a target. Typical takeoff roll for my Bonanza is 1100 feet near sea level. The halfway point is around 550 feet. Our runway has precision markings with 500 foot intervals. So I brief the takeoff to check my speed crossing the 500 foot marker and it should be close to 50 Kts, if it isn’t, I know early on that I have a problem and I cut the throttle and figure it out. You can do the same on any airplane, just adjust the speeds to match your liftoff speed and take 70% as your halfway speed. Then knowing your expected takeoff distance for your weight and density altitude, figure out a mark or point on the runway that is half that distance, Use passing that point to check your airspeed to see if it is normal, and abort if needed.

    On the other hand, a pilot should be able to safely takeoff and fly around the pattern and land without an operating ASI. Lift off by rotating to +7 to 10 degrees, use your normal power settings and flap settings and descend with your pitch set to anywhere between 0 and -5 degrees. PS, most instructors don’t have a good view of the ASI and do a lot of flying from the right seat without ever looking at it as they become familiar with knowing the normal attitude using visual cues. I guess after 5000 times around the pattern, you should learn something.

    Also, many pilots are not aware of the proper braking method if you have to make an emergency stop. It is imperative that you cut the power, apply light braking immediately to keep the nose on the ground, and then you pull the yoke to the full rear stop, sufficient to not allow the nose to come up as you apply more and more braking. Once the yoke is at the full rear stop, apply hard braking just up to the point short of the wheels stopping and skidding. It is best that you practice this maneuver before you need to use it. On most airplanes, by having the yoke at the rear stop your braking effectiveness is much greater than most pilots realize.

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  5. David A Hatcher on Sep 01, 2012

    It would be a real shame to crash a perfectly good airplane because of an inoperative airspeed indicator or worse yet, a bug. It’s like crashing your car into a tree to miss a squirrel. As pilots we cannot be distracted by such things to the point of losing control. Try this sometime, on a nice day don’t look at the airspeed indicator. Fly the pattern and land using power settings and attitude. I had a student absolutely freak because of a bug in the pitot tube. I made him fly the rest of the period with the airspeed indicator covered up. Orville, Wilber, Igor didn’t have a airspeed indicator.

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  6. Bob Watson on Sep 02, 2012

    I think I had the “fly with the airspeed indicator covered” exercise on my private and I definitely had to demonstrate that on my commercial. (But that was a while ago. Do they not teach that any more?)

    I like John’s idea of having a go/no-go speed distance; however, I thought twins (and larger aircraft) had such a concept for engine-out contingencies (v1). If you pass that speed you have committed to be flying because you’ve already determined that you can’t stop on the available runway. After you pass V1 (or the marker that John describes), you shouldn’t change your mind. It sounds like this pilot changed his/her mind.

    Granted, waiting for an airspeed that might never arrive because the pitot-tubes are covered (kick the tire and light the fire…) could be problematic and it makes having a distance marker a good backup.

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  7. n on Sep 02, 2012

    If it took him that long to catch it, just takeoff and land, you can feel speed well enough to know when a stall is coming, when your too fast etc.

    Prior to solo I used to like to get my students to fly a pattern with butcher paper on their panel, if a guy with under 20hrs can do takeoffs and landings without a panel, then, well.

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  8. Theodore Wilbar on Sep 26, 2012

    I would have aborted in this situation. considering that on your takeoff roll you should be making call outs for airpseed alive, and engine indications in the green and then usually i will glance over again on the rotation to verify. if the pitot cover was on and it still said 80 then he should have noticed it on the takeoff roll earlier than later.

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  9. Theodore Wilbar on Sep 26, 2012

    also bob most light twins do not have a v1 speed. thats usually for larger twins. most light twins have an accelerate stop distance and some will have an accelerate go distance as well.

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  10. superbird3000@yahoo.com on Oct 02, 2012

    This is a classic abort scenario. The pilot absolutely made the correct decision. There are a couple of factors to consider here:

    1) The force of impact going off the end of the runway (if that is your only option) is less than the force of impact coming down from a higher altitude at a higher rate of descent.

    2) If you aren’t getting reliable airspeed indications, then you have no way to guarantee that your airplane has any amount of energy. While it is easy to say that he should be able to “feel” the amount of energy on the airplane, that just is not practical in many heavier, higher performance aircraft that have very little warning prior to running out of airspeed.

    3) If you look at any well run Part 135 op, or any part 121 operation, you will find that they have VERY strict decision making criteria in terms of when to go and when to abort. While some of it is mandated, and they are legally required to have margins built in, it should be noted that much of the statistical difference in safety is due to those decision making criteria and built in margins.

    Either way, the accident statistics clearly point out that trying to make an airplane fly that isn’t ready to fly is nearly always worse than the alternative. Had the pilot elected to continue, those serious and minor injuries could have easily moved up into the fatality category.

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