Resulting Safety Initiatives

Although this accident occurred in 1978, regulatory development continued well into 1990's. This accident was the catalyst for a number of rule changes affecting runway performance, some of which have only recently been added to the certification requirements for transport airplanes.  

Tires

Photo of a B-747 at touchdown - Photo copyright Tim De Groot
Photo of a B747-400 at touchdown
Photo copyright Tim De Groot - used with permission

In response to NTSB Safety Recommendations A-78-67 through 74, the FAA has revised TSO-C62b to include updated tire rating criteria, performance standards, test requirements for re-treaded tires, and tire usage and mountings.

The revised TSO-C62b requires the manufacturer to furnish to the Manager aircraft certification office (ACO) having geographical purview of the manufacturer's facilities, the following technical data: speed rating, load rating, rated inflation pressure, tire size, width, outside diameter, mold skid depth, nominal loaded radius at rated load and inflation pressure, permissible tolerance on the nominal loaded radius, the actual loaded radius of the test tire at rated load and inflation pressure, weight, static unbalance of the test tire, wheel rim designation, manufacturer's part number and, for high-speed tires, a load deflection curve at loads up to 1.5 times load rating and a summary of the load-speed-time parameters used in the dynamometer tests. As used in this section, the term "high-speed tire" means a tire tested at a speed greater that 120 mph.

The manufacturer must also furnish the applicable maintenance and repair instructions that include inspection criteria for recapped tires to continue in service. Recapping procedures must be included along with any special repair procedures and special nondestructive inspection techniques applicable to that tire. TSO-C62b and TSO-C62c

In order to improve the capability of tires to withstand present operating loads, especially in large transport airplanes, a substantially revised series of dynamometer tests were imposed in TSO-C62c. These tests include a combination of high speed takeoff cycles, taxi cycles, an overload cycle, and overload taxi cycles, which are expected to result in major improvements in tire design with a significant increase in the safety level of high speed tires produced under the revised TSO.

(Goodyear Video: The Longest Runways

In addition, the FAA published Advisory Circular (AC) 145-4A, "Inspection, Retread, Repair, and Alterations of Aircraft Tires," dated July 10,2006, on qualification of retread tires that provides guidance for the development, qualification, and approval of aircraft tire repair and retread process specification, and the use of special nondestructive inspection techniques. The AC also provides information related to rule changes on aircraft tires used on transport category airplanes in order that tire reliability will be enhanced and the incidence of tire failures decreased. AC  145-4A

Photo of MD-11 landing - Photo copyright William Van Wanrooy
Photo of MD-11 landing
Photo copyright William Van Wanrooy - used with permission
Photo of runway in Hawaii - Photo copyright Quinn Savit
Photo of runway in Hawaii
Photo copyright Quinn Savit - used with permission

The FAA also published AC No. 20-97B, "Aircraft Tire Maintenance and Operational Practices," dated April 18, 2005, that provides recommended tire care and maintenance practices needed to ensure the safety of support personnel and the continued airworthiness of aircraft. Specifically, this AC provides guidance on the installation, inflation, maintenance, and removal of aircraft tires. In addition, this AC provides guidance on those operational practices necessary to maintain safe aircraft operations. AC No. 20-97B

Amendment 25-49, issued on November 21, 1979, revised 14 CFR 25.733 to include a 1.07 factor in establishing the required load rating of the tire on the airplane. When the load factor of 1.07 is considered in conjunction with the new overload takeoff test proposed in TSO-C62c for tires, this change effectively required high-speed aircraft tires to withstand an overload of 1.61 times the present load rating, a substantial upgrading of previous requirements.

Takeoff and Landing Performance Standard

(1) FAA rule changes mandated by:

Amendment 25-92 issued February 10, 1998, revised several sections of 14 CFR parts 25, 91, 121, and 135 concerning the methods for determining and applying the takeoff and landing performance standards for turbine-powered transport category airplanes.

The standards revised by amendment 25-42 require the accelerate-stop distance to include, in addition to the time delay associated with each deceleration device, two seconds of continued acceleration beyond V1 speed before the pilot takes action to begin stopping the airplane. This revision results in longer accelerate-stop distances being required for airplanes whose application for a type certificate was made after amendment 25-42 became effective. Consequently, turbine-powered transport category airplanes that are currently being manufactured under a type certificate that was applied for prior to March 1, 1978, have a significant operational economic advantage over airplanes whose type certificate was applied for after that date. This competitive disparity resulting from applying different performance standards has created a compelling need to amend the takeoff performance standards of part 25 without adversely affecting safety.

Amendment 25-42 was a broad brush approach, applying to all takeoffs, to increase the required accelerate-stop distance. This broad brush approach was taken because the takeoff performance standards do not explicitly account for many of the important operational factors that may affect takeoff performance. For example, amendment 25-42 standards did not distinguish between dry and wet runways, nor were the effects of worn brakes taken into account. Wet runways and worn brakes would result in an airplane requiring a longer accelerate-stop distance than with new brakes on a dry runway. By proposing to account for wet runways and to base stopping performance on brakes that are completely worn, these amendments would provide additional safety margins in the conditions where it is specifically needed in operational service.

Because wet runways and worn brakes would be accounted for in amendment 25-92, the FAA also proposed replacing the two seconds of continued acceleration beyond V1 with a distance equal to two seconds at V1. The distance equal to two seconds at V1, while shorter than that resulting from the continued acceleration beyond V1 required by amendment 25-42, is a distance margin that must be added to the accelerate-stop distance demonstrated during flight testing for type certification. This distance margin, based on the V1 speed and a time "delay" of two seconds, accounts for variability in the time it takes for pilots, in actual operations, to accomplish the procedures for stopping the airplane.

Photo of a B-747 lifting off
Photo of a B-747 lifting off
Photo copyright Stefano Rota - used with permission

Amendment 25-42 required the two seconds of time delay to be applied prior to the pilot taking any action to stop the airplane. This more restrictive approach caused the airplane to reach a higher speed during the accelerate-stop maneuver and resulted in a longer distance than the distance equal to two seconds at V1 speed. Inserting the time delay before the pilot takes any action to stop the airplane, however, did not accurately reflect the procedures that pilots are trained to use in operational service. Also, V1 is intended to be the speed by which the pilot has made the decision to reject the takeoff and has begun taking action to stop the airplane. The time it takes for the pilot to recognize the need for an RTO, which no longer exists once V1 is reached, is considered separately within the airworthiness standards. Therefore, the new amendments more accurately reflect rejected takeoff procedures and the intended use of V1 speed, and account for variability in the time it takes for pilots, in actual operations, to accomplish the procedures for stopping the airplane.

The purpose of the amendment 25-92 revising the takeoff performance standards of 14 CFR parts 25, 91, 121, and 135 was to rationally reflect the operational factors involved and thus reduce the impact of the standards on the competitiveness of new versus derivative airplanes. The new amendments also would require more restrictive standards to be met for takeoffs from wet runways than for takeoffs from dry runways. In addition, the accelerate-stop distance, which must be provided as an AFM takeoff limitation, is based on worn brakes rather than new brakes. Lastly, the airplane is assumed to maintain a constant velocity for the two-second time delay after reaching V1 speed (instead of accelerating). Overall, the amended standards are more rational and less restrictive than the existing standards, even though they remain slightly more restrictive than the standards that existed before amendment 25-42 became effective.

Amendment 25-92 revised the following parts of the 14 CFR 25:

1) Replace the two seconds of continued acceleration beyond V1 with a distance margin equal to two seconds at V1 speed;

2) Require that the runway surface conditions (dry or wet) be taken into account when determining the runway length that must be available for takeoff; and

3) Require that worn brakes be taken into account when determining the capability of the brakes to absorb energy and provide a stopping force for takeoff and landing.

This amendment revised several sections of 14 CFR parts 25, 91, 121, and 135 that provide the methods for determining and applying the takeoff and landing performance standards for turbine-powered transport category airplanes. Also, this notice proposes to amend part 1 to add a definition of the term "takeoff decision speed" and an explanation for the abbreviation "VEF."

Part 1 was amended to add a definition of the term "takeoff decision speed" and an explanation for the abbreviation "VEF."

Paragraph (i) of section 25.101 (14 CFR 25.101(i)) was amended to require that accelerate-stop and landing distances must be determined with all the airplane brakes at the fully worn limit of their allowable wear range.

14 CFR 25.105 was amended to require the airplane takeoff performance data be based on wet in addition to dry runways.

14 CFR 25.109 amended the method of determining the accelerate-stop distance prescribed by replacing the two seconds of continued acceleration after reaching V1 with a distance equal to two seconds at V1 speed. This would reduce the accelerate-stop distance that must be available for an RTO because the airplane would be assumed to begin stopping from a lower speed (V1 rather than the speed reached after two seconds of acceleration beyond V1).

14 CFR 25.109 was amended to provide the details of how the accelerate-stop distance would be calculated for a wet runway. This amendment contains a rational approach that includes consideration of the major variables affecting the stopping performance on a wet runway. This approach to determining the wet runway RTO performance includes: 1) taking into account the reduced braking force due to the wet surface; 2) permitting performance credit for using available reverse thrust as an additional stopping force; and 3) permitting a lower minimum airplane height over the end of the runway after takeoff. This approach would reduce the risk of overruns during RTOs on wet runways while retaining safety margins for continued takeoffs similar to those required for dry runways.

14 CFR 25.109 was also revised to permit the use of available reverse thrust when determining the accelerate-stop distance for a wet runway. "Available" reverse thrust is interpreted as meaning the thrust from engines with thrust reversers that are operating during the stopping portion of the RTO. Allowance for reverse thrust has been included because the most significant variable that affects the stopping performance on a wet runway, reduced braking friction, has been accounted for as part of the rational approach to wet runway RTO.

This amendment replaces the most costly and controversial aspect of amendment 25-42 with a requirement that closely represents the pre-amendment 25-42 criteria of 14 CFR 25.109, as applied to the certification of recent U.S.-manufactured airplanes.

14 CFR 25.113 was amended to allow the distance required for a continued takeoff from a wet runway to include taking off and climbing to a height of 15 feet, rather than the 35 feet required on a dry runway. This lower "screen height" (which is the height of an imaginary screen that the airplane would just clear with the wings in a level attitude when taking off or landing) reduces the balanced field length V1 speed, thereby reducing the number of high-speed RTOs on wet runways.

The FAA considers lowering the screen height to be an acceptable method of reducing the risk of overruns on wet runways because of the similarity to current rules when operating from dry runways that have a clearway. The minimum height permitted over the end of the runway for current dry runway takeoffs may be 13 to 17 feet, depending on the airplane, when a clearway is present. In addition, a 15-foot minimum screen height and vertical obstacle clearance distance has been allowed for many years by the British CAA for wet runway operations without any problems being reported.

The amended 14 CFR 25.113 did not permit the combination of clearway credit and a 15-foot screen height. 14 CFR 25.113 was clarified, however, to ensure that for wet runways the presence of a clearway does not result in the anomaly of requiring longer runway lengths than if there were no clearway.

14 CFR 25.115 was amended to permit the minimum vertical distance required between the takeoff flight path defined in 14 CFR 25.115 and obstacles (e.g., trees, hills, buildings, etc.) would be reduced by a corresponding amount. To accomplish this, CFR 25.115 would be revised to state that the takeoff flight path shall be considered to begin at a height of 35 feet at the end of the takeoff distance.

This revised definition of the takeoff flight path would apply equally to dry and wet runways, even though the height at the end of the takeoff distance (i.e., screen height) for wet runways is only 15 feet. The effect of this amendment is to permit the flight path information currently contained in the AFM for dry runways to also be used for wet runways. Because of the reduced screen height, at a given point in the flight path, the height of an airplane taking off from a wet runway will be approximately 20 feet lower than the height of that airplane taking off from a dry runway. Therefore, using the flight path information currently in the AFM will reduce the airplane's actual height over obstacles by approximately 20 feet when the airplane takes off from a wet runway.

Prior to amendment 25-92, regulations required the airplane's flight path to be higher than any obstacles by a combination of an increment of height and an increment of gradient (i.e., the slope of the flight path). This amendment reduces the height increment by approximately 20 feet, but the gradient increment is not changed. As the distance from the end of the takeoff distance increases, the gradient increment provides an increasingly greater portion of the total height difference between the airplane and the obstacle. Therefore, the effect of reducing the height increment over obstacles by 20 feet diminishes as the distance from the end of the takeoff distance increases.

Paragraph (f)(3) of section 25.735 (14 CFR 25.735(f)(3)) was amended to require that the brake energy capacity rating must be determined with each brake at the fully worn limit of the allowable wear range. 14 CFR 25.735 was also amended to add a requirement for a flight test demonstration of the maximum kinetic energy rejected takeoff with not more than 10 percent of the allowable brake wear range remaining.

Manufacturers or operators of previously certificated airplanes may elect to comply with these proposed later amendments by a change to the type design, and thus the benefits of the revision to the time delay criteria of 14 CFR 25.109 would be available to relieve the economic burden imposed by amendment 25-42. The more rational accounting for reduced stopping capability on wet runways during RTO and for the reduced capability of worn brakes would also be included in such a recertification. It is expected that, for airplanes whose certification basis includes amendment 25-42, applicants will elect to comply with this proposal because it will be economically beneficial for them to do so.

Paragraph (b) of section 25.1587 (14 CFR 25.1587(b)) was amended to require that performance information for wet runways be included in the AFM. The AFM contains, along with other information, all of the performance information computed under the provisions of 14 CFR part 25.

14 CFR 91.605, 14 CFR 121.189, and 14 CFR 135.379 of the operating rules were amended to require that wet runways be taken into account when determining the runway length that must be available for takeoff, if wet runway performance information exists in the AFM. Thus, this rule would apply only to airplanes whose application for type certification occurs after the rule becomes effective.

Evacuation Slides

In response to NTSB Safety Recommendations A-79-16, A-79-18, and A-79-19, the FAA undertook research and development testing which resulted in the issuance of new TSO-C69 slide and slide/raft fire resistance requirements, girt strength, and critical angle testing.

TSO-C69a, TSO-C69bTSO-C69c

1) TSO-C69a, "Emergency Evacuation Slides," dated June 3, 1983, included the following changes:

  • Added new radiant heat testing requirements of inflatable emergency evacuation slide/raft material. The test required three specimens tested at 1.5 BTU/ft2 sec, and the resultant times to failure in which average time to failure must not be less than 90 seconds. Time to failure is the time between first application of heat to the specimen and first drop in pressure below the maximum pressure attained in the test cylinder during the test.
  • Updated the slide/raft material flammability requirements to comply with paragraph (b) of section 25.853, "Compartment interiors," (14 CFR 25.853(b)).
  • Revised the slide/raft strength requirement: "The device, installed at its critical angle, may not collapse when loaded to its maximum capacity as determined by a test in which a sufficient number of adult (170 pounds or more) evacuees crowd closely in line at the top of each lane of the device and jump into the device in rapid succession at a rate not less than one evacuee per second per lane. It must demonstrate the means used to connect the device to the airplane (girt material) will not fail when the device is operated at low angles (from horizontal) and at maximum evacuee loading conditions (including asymmetrical loading) expected in service. Also, the angles and loads selected may not be greater than 30 degrees and less than 1,050 pounds per lane, respectively. If the device is equipped with outrigger pontoons, additional test loads must be applied to account for asymmetrical loads that would result from evacuees inadvertently entering the pontoon areas during an emergency evacuation.
Photo of slides deployed Photo of slides deployed
Photo of slides deployed
Photo copyright Yusu Ren - used with permission
Photo copyright Ronen Eckstein - used with permission

Additional Slide/Raft requirements beyond the NTSB recommendations were also initiated by the FAA to increase passenger/crew survivability

  • Evacuation rate increased from 30 evacuees to 60 evacuees per minute per lane at representative sill heights for a duration of at least 70 seconds.
  • Inflation time decreased from 25 seconds to 10 seconds after the actuation of the inflation controls begins. An additional wing-to-ground slide now requires the device to automatically erect in 15 seconds after actuation of the inflation control.
  • Slide/raft devices must be equipped with side guards or other means to prevent evacuees from accidentally missing or falling from the device.
  • Self illuminated slides must be designed so the illumination means is activated automatically during deployment or inflation and the level of illumination meets the appropriate requirements in 14 CFR 25.812.
  • Slide/raft must have the capability, in 25-knot winds directed from the most critical angle, to deploy and with the assistance of only one person, to remain usable after full deployment to evacuate occupants safely to the ground.
  • At least five consecutive deployment and erection tests must be demonstrated without failure to ensure that the slide/raft device performs its intended function. Section 25.809, "Emergency exit arrangement," (14 CFR 25.809) contains requirements pertaining to the deployment and erection characteristics as well as the installation of the device on the airplane, which may be taken into consideration along with the requirements of this TSO.

2) TSO-C69b Emergency Evacuation Slides, dated August 17, 1988, revised:

  • Inflation time to decrease from 10 seconds to 6 seconds after the actuation of the inflation controls begins. An additional wing-to-ground slide now requires the device to automatically erect from 15 seconds to 10 seconds after actuation of the inflation control.

3) TSO-C69c Emergency Evacuation Slides, dated August 18, 1999, revised:

  • The slide/raft material flammability requirements to comply with paragraph (a) of 14 CFR 25.853(a) and the criteria described in paragraph (a)(1)(ii) of Appendix F, part I, of 14 CFR part 25.
  • Evacuation rates to increase from 60 evacuees to 70 evacuees per minute per lane at representative sill heights for a duration of at least 70 seconds.
  • Radiant heat testing requirements of inflatable emergency evacuation slide/raft material. The pressure holding materials in the device must meet the 90-second minimum-time-to-failure requirement and the 180-second average-time-to-failure requirement of the radiant heat resistance test.

(Aircruiser Slide Deployment video)

(Boeing Model 777 evacuation demo video)

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