46
Jack Ledford
Johnson
Recommendations on Changes in Operating
Procedures Resulting from Aircraftccident.
Dear Jack:
In the last severalave studied Intensively all aspects which led to the loss ofnd have investigated what steps should be taken to remove tbe causes which led to this accident.
The cause of the accident was that the wiring to the pitch and yaw gyros in the stability augmentation system was reversed, which made theuncontrollable immediately upon lift-off. The accident board has provided you with the statements of those involved in all phases of this regrettable accidento not intend to elaborate on their findings here. ould like to present my views on steps that should be taken to prevent mis-wiring in the control system in the future.
A. Prior to resumption ofecommend that thesteps be taken.
will install riveted type collars on the pitchcabling connectors. These will make it impossible for them to
be incorrectly installed on the yaw rate gyro. Theimilar type of collar which currently Is assembled using screws. I'm afraid that these can bo readily removed and we should go to the riveted type.
addition tonch high lettering which is onscaling which is the pitch and which is the yaw cable, wecode the cable assembly In the gyro box. All gyro packagespainted with yellow for the yaw gyro and blue for the pitchon these units in large letters will be the properand "yaw." hould state that the gyro packagesa name-plate which differentiates pitch and yaw, but thesmall.
New ground wires will be installed, as we. have found several in our inspections which have been worn in service.
Our maintenance manual will be amended toadditional detail on all phases of removal, installation and checkout of the SAS.
We haverocedure whereby withhydraulic power on the aircraft the over-all end-to-endthe yaw channel can be checked readily. This is done bymounting screws on the yaw gyro and rotating the gyro cania enough play in the bolt holes to allow gyro operation of theto the extent ofnch travel Cm the leading edge.
1). We are investigating the possibilityimilar simple check on the pitch channels but have not completed our tests.
c. o not recommend that these be pre-fllght checks, but they ahould be done always when the SAS gyros or wiring havo been worked on. o not know of any reasonable check which can be donere-fllght test with the current equipment, although we will continue to investigate the possibilities ofeasonable test which will not subject tho gyros to damage in the course of testing.
written inspection procedure will be devised toproper inspection and witnessing of the removal,checkout.
oncurrently with the above, we are undertaking theprogram.
An investigation of all other installations which affect flight safety where wires or plumbing can be Interchanged eaaily. houldou that last summer weomplete program of color coding all important wires and plumbing connections In the Unfortunately, many of these items were not done during the modification program on2 vehicles. We have had one case where the color coding was applied Improperly whichalse hookup In the landing gear circuit. elieve, nevertheless, that color coding Isesirable thing to do.
We arc investigating whether or not wires to thovalves can be interchanged and, if so, what would result. We arc looking particularly at the pitch and roll transfer valves on tho inboard elevon servos and the LVDT's.
The landing gear selector valve and the landing gear door valve are identical type units and might be improperly wired. This would leadlosing of the inboard doors without operation of the main landing gear. Whileafety-of-flight item, steps will be taken to provent mis-wiring of these valves and, of course, our procedure for operating the landing gear on the ground whenever any work is done on the gear should prevent mis-wiring.
Our investigation lias turned up the facta that the noee hatch seal lever in the cockpit can be installed two different ways, one of which is incorrect. We willodification to prevent this,
The pitot static valve lover in the cockpit and associated linkages and valves can be assembled incorrectly. If our instructions are not followed.
Ground test selector valves onay and cockpit pressure regulators can be mis-installed. This could result infailure in flight. We will correct this.
You might consider that the above indicates very serious designin many areas of the aircraft. This is not true. For instance, the wires which were mis-located on the improper SAS gyros are marked "pitch" and "yaw",while the individual plugs coming out of the main cablos are marked for "pitchpitchpitchith similar markings for the individual plugs to the yaw gyro. The gyro packages themselves have nameplates indicating their functions and there is additional marking on the individual plugs indicating whether they,, for both the pitch and yaw final connectors. These are matched by similar indications on the gyro cables. Likewise, the usual aircraft practice of numbering individual wires was followed to make connections to the pinB at the plugs. This is true In all the otherave noted above, but we are finding as our aircraft become more and more complex that we have an increasing problem training evenpeople to follow good practice.
For instance, the inspector who signed off the installation on6 we considered toompetent inspector, having some seventeen years of experience in the aircraft business. The mechanic whoup the wires improperly had seven years of experience and much of it on aircraft with complicated electrical systems, such as the Constellation.
It is unfortunate that some time back, in order to keep from damaging the, with our concurrence, elected to goheckout of the wiring in the SAS system which did not carry through to the point where the surfaces were actuated. In fact, we still have on somea means for mechanically operating the gyrosanner which can be used to sec the actual control deflections. This system, however, also depends upon careful operation by the operator and led to problems in re-setting the gyros to their zero position and, in certain cases, were usedanner to effect hard-over signals, which damaged the gyros.
At the present time,or we are prepared to recommendnd-to-end" pre-flight check which can be applied readily to the existing system. We do, however, agree that the means proposed above should be used to chock out the system when the gyros have born removed or the wiring in the gyro cans disconnected.
Inool that the changes made in the gyro cabling andtogether with the yaw gyro check,omplete answer to the problem of mls-wlring which caused the accident to
CLJ:vmp
Original document.
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