Aircraft Accident Report: United Airlines Flight 227/Attachment B

by C. S. Murphy, R. T. Murphy, G. J. Minetti, W. Gillilland, & J. G. Adams, Civil Aeronautics Board

ATTACHMENT B

B-80-96

NOV 30 1965

Mr. George S. Moore
Director
Flight Standards Service
Federal Aviation Agency
Washington, D. C. 20553

Dear Mr. Moore:

Our investigation of the November ll, 1965, accident of United Air Lines Boeing 727, N7030U, at Salt Lake City, Utah, has progressed to the point where we believe specific recommendations are in order in regard to the routing of fuel and electrical lines through the fuselage. We will probably have additional recommendations later concerning other design and operational aspects; however, further investigation and study are required beforehand.

It has been established with reasonable certainty that the fire following impact resulted from fuel lines being broken by the failed right main landing gear. This component broke through the fuselage sidewall in the vicinity of fuselage station 1050 and severed the fuel lines to the No. 2 and No. 3 engines. Ignition of spilled fuel could have been caused by sparks from runway contact or by a broken and shorted generator lead, or both. As you well know, the fire which followed was devastating and resulted in the loss of 43 lives.

It is interesting to note that in this accident both main landing gears struck the sidewalls of the rear fuselage after being broken free from their attachments. This directly rearward path of both gears indicates that the aircraft was not yawed appreciably at the time of impact and, therefore, we believe it is indicative of the natural failure pattern for any straightforward hard impact. In the past there have been many cases of landing gears being torn from aircraft because of low approaches over dikes and other obstructions and because of landings short of runways followed by the curbing of the gear on the paved runway end. Since there is no reason to believe that the 727 will not be subjected to similar treatment, it is imperative to afford a higher-degree of survivability following such accidents. We, therefore, make the following recommendations:

1. Fuel lines through the fuselage should be rerouted that they pass through the floor beams near the centerline of the aircraft.

2. The fuel lines and their shrouds should be made of stainless steel and should have a wall thickness of sufficient dimension to withstand rather severe impacts. We suggest that the wall thicknesses be not less than 0.040 inch.

3. The generator leads should be routed so that there is maximum separation between these leads and the fuel lines. Each lead should be in a separate plastic conduit with suitable strength and flexibility to withstand bending and reasonably high tensile load.

In regard to recommendation No. 1 above, it should be pointed out that his aircraft struck the ground with a recorded impact of 8.9 g's after the landing gear failure but despite this heavy impact the aft fuselage belly structure did not collapse; In other words, had the fuel lines been running through the center area of the floor beam, they would have been adequately protected. In support of recommendation No. 2, it was noted during the investigation that although the aluminum tubing and shroud of fuel line No. l did not melt, those of lines No. 2 and No. 3 did melt in areas other than the break points. Thus, fire from one broken line could melt through the present aluminum tubing and shroud of another line and thereby increase the intensity of an existing fire.

It is our understanding that both FAA and Boeing personnel who participated in the investigation of the Salt Lake City accident have made similar recommendations through their own organizational channels.

We also recommend that all other similarly configured aircraft (e.g., DC-9, Lear Jet, Caravelle, BAC 111, Jet Commander) be the subjects of a study to determine whether or not analogous dangers exist in their fuel and electrical system geometries.

Should your staff desire further information or wish to discuss the problem further, we can make appropriate members of the investigating team available at any time.

Sincerely yours,

/s/ B. R. Allen

B. R. Allen
Director, Bureau of Safety

COPY

November 30, 1965

Mr. George S. Moore
Director
Flight Standards Service
Federal Aviation Agency
Washington, D. C. 20553

 

Dear Mr. Moore:

The United Air Lines Boeing 727 aircraft accident at Salt Lake City, Utah, on November 11, 1965, disclosed the possibility of mal-operation of the emergency lighting system which failed to illuminate the emergency exits for passenger escape to safety. To date there has been no substantiation of any lighting in the cabin area after the aircraft came to rest.

The system is designed to be operated by a three-position switch in the cockpit overhead electrical panel. An amber indicator light adjacent to the switch monitors switch position and availability of 28 V DC power from battery bus.

OFF	—	lights "OFF," batteries not charging, indicator light "ON."
ARMED	—	lights "OFF," batteries charging if AC and essential DC power available, indicator light OFF. If AC and battery bus DC power fails, lights "ON." Indicator light remains "OFF."
ON	—	lights "ON," batteries-discharging, indicator light "ON."

However, if the switch is left in the "ARM" position and the DC battery bus is still a complete circuit, the lights will-remain "OFF." This is the situation that undoubtedly took place.

To eliminate this physical operation during a period of emergency, it is recommended that a procedure be used so that the emergency lights are turned "ON" during all takeoff and landing operations of Boeing 707, 720, and 727 aircraft, as well as all other turbine powered aircraft with automatic emergency lighting systems. Also, the aircraft should be rewired so that a loss of electrical power source for normal cabin lighting activates the emergency lighting. The reverting to the self-contained nickel batteries in event of complete loss of aircraft electrical power should be retained.

It is further recommended that a study of all other type aircraft be made to ascertain the operating features of their emergency and exit circuitry to assure the emergency lighting operating during any emergency.

The above was discussed with your Airframe Section electrical engineer, Mr. E. Heil.

Sincerely yours,

/s/ B. R. Allen

B. R. Allen

Director, Bureau of Safety

COPY

B-80-96

DEC 16 1965

Mr. George S. Moore
Director
Flight Standards Service
Federal Aviation Agency
Washington, D. C. 20553

Dear Mr. Moore:

This is a further recommendation based on our investigation of the United Air Lines Boeing 727, N7030U accident at Salt Lake City, Utah, on November 11, 1965. As you know, 43 of the 91 occupants died as a result of this accident. Our preliminary findings indicate that none of these fatalities were due to traumatic injuries but all died from suffocation during the resultant fire. This is evidenced by the elevated carboxyhemoglobin concentrations in the victims and lack of trauma.

We are conducting an extensive study in the human factors area to determine how the survivors evacuated the airplane, the difficulties they experienced and the time it took them to evacuate. It is hoped that we will be able to determine the fire progression in the occupiable area of the cabin. Preliminary information indicates that the interior furnishings contributed greatly to the spread of fire and the emission of heavy black smoke, both of which contributed to the fatalities.

We understand that the Aircraft Development Service of FAA has just completed a study of air transport passenger cabin fires and materials and that their report will be published shortly after the first of the year. We have been advised that the aforementioned fire tests have disclosed a number of deficiencies in the materials presently being installed in aircraft interiors and that materials are available which would be far superior to those being used today.

We do not have complete information regarding the testing methods used during the aforementioned study by the Aircraft Development Service. We believe that the toxicity of the resultant gases produced by the combustion of various combinations of materials used in aircraft interiors might be worse than those produced by the materials individually. If the tests did not include such determinations it is recommended that they be expanded to test various combinations. Additionally these combinations should be tested with fuels carried in aircraft.

The Federal Aviation Regulations, in our opinion, should be updated to require newly certificated airplanes to be fitted with these newer materials which have been found to be less susceptible to combustion. Additionally, it is recommended that the air carriers be strongly encouraged to utilize these materials when they refurnish their airplanes.

Upon completion of our factual report on this evacuation we will forward a copy to you. In the interim, if additional information is desired, feel free to contact Mr. Doyle in our Human Factors Section.

Sincerely yours,

/s/ Robert L. Froman

for B.R. Allen
Director, Bureau of Safety

COPY

FEDERAL AVIATION AGENCY
Washington, D. C, 20553

January 13, 1966

Dear Mr. Chairman:

This is in reference to letters from the Director, Bureau of Safety, Civil, Aeronautics Board, two dated November 30, and one dated December l6, 1965, containing recommendations resulting from your investigation of the United Air Lines, Boeing Model 727 accident at Salt Lake City, Utah, on November 11, 1965. These were acknowledged respectively, on December 8, 10, and 27, 1965. We have studied your recommendations and are pleased to report that we have had many of them under consideration for some time. As you know, the details of many of the points will take time and resources to fully reconcile, but will be resolved as soon as possible.

The Agency safety program relative to the areas mentioned in your letters is outlined below:

Fuel lines and generator leads

Concerning your recommendation to relocate the fuel lines in the Boeing 727 near the centerline of the aircraft, our evaluation of this indicates the present location is the best possible because the lines are surrounded by the heaviest structure available in their present locations. If the fuel lines are moved inboard toward the center of the airplane, they will then be susceptible to rupture by items in the cargo compartment in the event of a belly landing which is the more conventional type of damage anticipated in emergency landings. We note in the Salt Lake City accident that the bottom of the fuselage was crushed upward approximately 20 inches. It is for this reason that the fuel lines were initially located in their present position. It is recognized that the fuel lines can be strengthened and their resistance to impact or shearing type failures can be improved. Engineering design studies are now in process to develop such improved type lines on a retrofit basis.

In regard to your recommendation to use stainless steel lines and shrouds, the redesigned configuration being studied is expected to include a neoprene core, stainless steel sheathing, and a teflon-type covering The aluminum alloy shrouding will be retained since it is less prone to cutting or shearing of the fuel lines.

With reference to your recommendation to relocate the generator leads, the present electrical leads in the area of the fuel line will be rerouted to a near center position in the fuselage to separate them as far as practicable from the fuel lines. A teflon type cover is being considered for the generator leads so that even if the bus is ruptured due to an impact load, the flexible cover will remain intact under deflection and thus reduce the likelihood of ignition of a fire.

We note your observations concerning landing gear failure on the Boeing 727. An engineering review of the landing gear design has been completed and the conclusion reached that a corrective measure is needed. The change will improve the response rate of the upper side brace tube attachment fitting so that without reducing the strength of this fitting for normal loads, the attachment fitting will fail after a small angle rotation toward the rear. A retrofit design change is in process.

Emergency cabin lighting systems

With reference to your recommendation concerning emergency lighting system operation and design, the emergency cabin lighting circuitry is being looked at very carefully. The present system provides for the battery powered emergency lights to go on after an interruption of either DC or AC power. The burning of the emergency lights during each takeoff and landing would deplete the batteries which have approximately 20 minutes capacity. The recharging rate would not be sufficient to assure emergency lights when needed. Our evaluation has not yet been completed of the full impact of the re-engineering and modification of systems to provide the capability of manually turning on emergency exit lights using airplane power during each-takeoff and landing. Our attention will be given to similar designs in other transport aircraft.

Flammability of cabin interior materials

The Agency endorses and has recognized the need for more stringent requirements to define the characteristics of cabin materials when exposed to fire. Research action to improve these standards was initiated in early 1963 to investigate this problem. Subsequently Federal Aviation Agency Technical Report No. ADS-3, dated January 1964, and entitled "Flammability and Smoke Characteristics of Interior Aircraft Materials," served as part of our basis for a related regulatory project. Proposed new fire protection standards for aircraft cabin interior materials are being processed by the Agency to require self-extinguishment burn characteristics for such materials on transport aircraft. Our research effort is also being applied currently to toxicity and smoke propagation characteristics of all materials used in transport airplane interiors and may well lead to further proposals to amend the related airworthiness standards. These projects are identified as "Thermal Criteria for Interior Materials" and "Hazardous Combustible Characteristics of Cabin Interior Material."

From the foregoing, I believe you will agree that evaluation of the need for corrective action on the Boeing 727 series aircraft is well underway. I would also like to make it clear that while the attention is focused on the Boeing 727 series, our consideration will also be given to other transport aircraft. Reassessments of transport aircraft with engines mounted in the rear are presently in process and may well lead to their further improvement.

Every effort is being directed by the Agency to continuously seek improvement of crashworthiness safety features. In consonance therewith, we are reactivating our task force to again reevaluate the adequacy of such provisions in transport airplanes and related operating procedures. This is timely as a followup to our recently adopted emergency evacuation rules. As part of this program, you will also be interested in knowing that the Agency plans to hold a series of meetings in the coming weeks with all segments of industry to stimulate constructive ideas for improvements in crashworthiness standards. As your Mr. Bernard Doyle was a member of the original task force, we would be pleased to have him participate as an advisor.

In summary, may I state the Agency is acutely aware of the need to continuously seek improved crashworthiness standards, and to improving the means to evacuate passengers under the most extreme conditions. We shall continue to devote our maximum efforts toward these objectives. It is extremely gratifying to me to know that the actions which the Agency either has had under consideration, or now is contemplating, have your support.

Sincerely,

/s/ William F. McKee

WILLIAM F. McKEE
Administrator

Honorable Charles S. Murphy
Chairman, Civil Aeronautics Board
Washington, D. C. 24028