Touchdown Zone

Touchdown Zone

Touchdown Zone

Three reports from the NTSB:

Surveillance video revealed the Cessna Citation 550 touched down about 1,700 feet past the runway threshold of the 5,000-foot-long runway and that the thrust reversers were not deployed during the recorded portion of the landing roll. The airplane’s tires left over 1,300 feet of skid marks before it overran the departure end of the runway. Post-accident testing of the brakes revealed no evidence of any mechanical anomalies. Based on the available evidence, it is likely that the pilot landed the airplane well beyond the runway threshold and did not apply adequate braking effort until insufficient runway remained to stop the airplane on the paved surface. The National Transportation Safety Board determines the probable cause(s) of this accident to be the pilot’s failure to attain the proper touchdown point and to adequately slow the airplane within the available runway, which resulted in a runway overrun. 

After the Eclipse EA500 touched down on the 4,422-feet-long runway, the airline transport pilot applied the brakes to decelerate; however, the brakes were not operating. He continued “pumping the brakes” and considered conducting a go-around; however, there was insufficient remaining runway to do so. The airplane subsequently continued off the end of the runway, impacted a berm and came to rest upright. Examination revealed no evidence off any preimpact anomalies with the brake system that would have precluded normal operation. According to data downloaded from the airplane’s diagnostic storage unit (DSU), the airplane touched down 1,280 feet beyond the runway threshold, which resulted in 2,408 feet of runway remaining (the runway had a displaced threshold of 737 feet) and that it traveled 2,600 feet before coming to rest about 200 feet past the runway. Comparing DSU data from previous downloaded flights revealed that the airplane’s calculated deceleration rate during the accident landing was indicative of braking performance as well as or better than the previous landings. Estimated landing distance calculations revealed that the airplane required about 3,063 feet when crossing the threshold at 50 feet above ground level. However, the airplane touched down with only 2,408 feet of remaining runway, which resulted in the runway overrun. The NTSB determines the probable cause(s) of this accident to be the pilot’s failure to attain the proper touchdown point, which resulted in a runway overrun.

The pilot of a Beech Baron 58 initially intended to perform a GPS approach to Runway 23, into the wind. However, the weather was below minimums for that approach, and he elected to perform an ILS approach in the opposite direction to Runway 5. While about 100 feet above decision height, the pilot did not have the runway environment in sight and started to go around but did not increase engine power. He then observed the runway centerline markings and, due to excess speed and a tailwind, the airplane floated and landed long. Touchdown was about 1,000 feet before the departure end of the 7,001-foot-long runway at a speed of 85 knots. The pilot applied the brakes but the runway was wet and he did not feel deceleration. The airplane traveled off the end of the runway, coming to rest upright in a grass area. The pilot stated there were no preimpact mechanical malfunctions with the airplane. Weather at the time of the accident included an 11-knot tailwind. The NTSB determines the probable cause(s) of this accident to be the pilot’s failure to maintain a proper glidepath and failure to perform a go-around once a safe landing could not be accomplished, which resulted in a landing area overshoot and runway excursion. 

 There are mitigating factors in each of these accidents, and the numerous others like them that happen all too frequently in twin and turbine aircraft. Wet runways. Tailwinds. Low visibility. Excessive speed. Improper or ineffective braking. Regardless of the contributing factors, however, all accidents of this type have one thing in common: The pilot did not command the airplane to land in the appropriate runway touchdown zone. 

Except in unusual cases, the accepted runway touchdown zone is:

  • Approximately 1,000 feet from the runway threshold, or 
  • At one-third of the total usable runway length, when that usable length is less than 3,000 feet. 

On paved runways with an instrument approach an “aiming point” may be marked with large white markers if the runway is longer than 900 meters (close to 3,000 feet). On these runways, additional “hash mark” stripes are painted 500 feet before and 500 feet after the aiming point marking, defining the limits of the touchdown zone.

Regardless of the runway, you should positively identify the touchdown zone when landing. The trick is to land in that zone so that there is sufficient runway remaining to bring the airplane to a stop well within the calculated landing roll distance taking into account environmental and runway conditions, properly operating braking systems, and correct pilot technique. 

This brings two vital, often overlooked points: 

  1. Required runway length does not equal calculated landing distance. Available runway begins at your touchdown spot, so it’s the distance from that point to the end of the runway that must be compared to calculated landing distance.
    Generally, this means adding 1,000 feet to the calculated distance to arrive at a minimum runway length, because you’ll overfly the first 1,000 feet aiming for your touchdown spot. Also, you may land a little beyond your aim point but still be within an acceptable touchdown zone, and if you’re like me, you’ll likely use something less than test-pilot-optimum braking technique once you’re on the ground, so you probably want to pad your ground roll requirement by at least 50 percent. Your minimum acceptable runway length, then, may be:
    (Calculated ground roll distance x 1.5) + 1,000 feet
  2. Deciding whether to go around or to continue a landing attempt can’t happen after you’ve touched down with doubts about remaining runway length. It shouldn’t happen during your landing flare. No, your go-around decision should be made on short final before you begin your flare based on measurable data that will predict whether you’ll land in your touchdown zone.

Even if you’re aimed precisely for ground contact at your aim point, it does you no good – and a lot of harm – if the airplane is not properly configured for landing and in the proper energy state to safely land and come to a stop. These are the things you can judge before you begin your landing flare. If you are not on speed, in landing configuration, on glidepath to the touchdown zone, at the proper vertical speed, and aligned with the runway centerline before you begin your flare, go around. Don’t wait until later to decide; don’t try to fix the errant condition(s) as you transition to flare; and don’t try to “salvage” an approach (considering all connotations of the word salvage as it might apply to a botched landing). Here are some considerations as you pass through Decision Altitude (200 to 400 feet above runway threshold height) regardless of the type of instrument or visual approach you’re flying:

  • Airspeed. Generally, this is 1.3 times the stalling speed in the airplane’s current configuration at its current weight. This may be a computed or tabulated indicated airspeed from the Airplane Flight Manual (AFM) or Pilot’s Operating Handbook (POH).  
  • Angle of attack, if an AoA sensor is installed. If the AFM or POH calls for flying a specific AoA on short final, or an aftermarket AoA device contains specific indications to attain on short final, then this becomes your target. If your AoA indicator is supplemental you may determine an approximate AoA display pattern from experience. 
  • Attitude. Pitch attitude, whether out the windows or on an attitude indicator or Primary Flight Display, will be consistent for a given indicated airspeed and/or AoA at a given center of gravity location and airplane configuration (flap and landing gear position). 
  • Airplane configuration is correct for landing: gear down, flaps set.  
  • Power is as expected for the landing. Performance results from the proper combination of indicated airspeed and vertical speed at the correct power or thrust setting.
  • The airplane is on glidepath and aimed to a landing in the runway’s touchdown zone.  
  • The airplane’s vertical speed is on target to carry the airplane on glide path from where you are to the touchdown zone.  

Runway overruns are disappointingly common in piston twins and turbine airplanes. In almost all cases they’re preventable and even predictable if you know what to look for before beginning your landing flare. Measure yourself against these variables as you pass through Decision Altitude; failure to attain any of those variables by this point means an increased risk of runway overrun and calls for an immediate
go-around.  

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