A-81-108
NTSB Safety Recommendation — Aviation
Recommendation text
THE NTSB RECOMMENDS THAT THE FEDERAL AVIATION ADMINISTRATION: INCORPORATE THE FOLLOWING INFORMATION IN THE DC-9 SERIES -10 THROUGH -50 TRAINING MANUALS AND PROGRAMS UNDER THE FLIGHT CONTROL AND LANDING SECTIONS: WHEN THRUST REVERSERS (LOCATED JUST FORWARD OF THE VERTICAL STABLIZER) ARE USED DURING LANDING ROLLOUT, THE EXHAUST GASES FROM THE ENGINES ARE DEFLECTED BY THE THRUST REVERSER BUCKETS IN SUCH A MANNER THAT THE FREE STREAM AIRFLOW OVER THE VERTICAL STABLIZER AND RUDDER IS BLOCKED, REDUCING THE EFFECTIVENESS OF THESE SURFACES. AT A NOMINAL AIRSPEED OF 100 KIAS, THE REDUCTION IN RUDDER EFFECTIVENESS WITH INCREASING SYMMETRIC REVERSE THRUST LEVELS IS SHOWN BELOW. ENGINE THRUST MAXIMUM RUDDER SETTING EFFECTIVENESS AVAILABLE(PERCENT)*/ FORWARD IDLE 100 REVERSE IDLE 65 1.3 EPR (REVERSE) 25 1.6 EPR (REVERSE) MINIMAL */RUDDER EFFECTIVENESS ALSO DECREASES WITH DECREASING AIRSPEED. ON A DRY RUNWAY, DIRECTIONAL CONTROL IS EASILY MAINTAINED BY DIFFERENTIAL ANTISKID BRAKING AND NOSEHWEEL STEERING. HOWEVER, UNDER ADVERSE CONDITIONS SUCH AS A SLIPPERY RUNWAY WITH RAIN, SNOW, OR ICE, WHEN CROSSWINDS REDUCE THE BRAKING EFFECTIVENESS OF THE GEAR ON THE UPWIND WING, OR WHEN A HIGH-SPEED LANDING IS MADE WITH BOTH HYDRAULICS SYSTEMS OUT (I.E., FLAPS/SLATS RETRACTED, GROUND SPOILERS, RUDDER HYDRAULIC BOOST, NOSEWHEEL STEERING ALL RENDERED INOPERATIVE, AND BRAKE ANTISKID SYSTEMS LIMITED BY HYDRAULIC ACCUMULATOR PRESSURE), THE VERTICAL STABILIZER AND RUDDER WILL BE THE PRIMARY SOURCE OF DIRECTIONAL STABILITY AND CONTROL DURING THE HIGH SPEED PORTION OF THE LANDING ROLLOUT. UNDER THESE CONDITIONS, IT IS IMPORTANT TO MAKE ALLOWANCE FOR THE ADVERSE EFFECTS OF REVERSE THRUST ON THE EFFECTIVENESS OF THE VERTICAL STABLIZER AND RUDDER.
In plain language (FlightFinder summary)
The NTSB asks the FAA to add information to DC-9 series -10 through -50 training materials explaining that when thrust reversers are used during landing rollout, the exhaust gases block airflow over the vertical stabilizer and rudder, reducing their effectiveness. The text provides specific data on rudder effectiveness loss at various reverse thrust levels and airspeeds, and notes that under adverse conditions like slippery runways or system failures, directional control relies heavily on the vertical stabilizer and rudder, making it important to account for these effects.
This plain-language summary is written by FlightFinder to explain the recommendation above. It is not the official wording — the verbatim NTSB text is quoted above.
Details
| Status | Closed - Acceptable Action |
|---|---|
| Mode | Aviation |
| Closed | Nov 2, 1984 |
| NTSB number | LAX80FA111 |
| Addressees | FAA |
External links
NTSB safety recommendations are advisory; addressees are not legally required to adopt them. Source: NTSB CAROL (public domain).