Maintenance and Certification
- ISSUE 1/2008
- Copyright and Credits
- Guest Editorial
- To the Letter
- Flight Operations
- Recently Released TSB Reports
- Maintenance and Certification
- Accident Synopses
- Regulations and You
- Pilots Beware: Geese Are in the Air
- Aviation Safety in History
- Take Five: Snow Landing and Take-off Techniques for Helicopters
- Full HTML Version
- PDF Version
- Inspection Levels Part 1: How Closely Should We Look?
- Inspecting Airplanes on the Ramp-The Role of the Canada Border Services Agency (CBSA)
- Two Cases of Reversed Flight Controls
This is the first of three articles on the topic of inspection levels.
Most of the inspection tasks called up in a large aircraft maintenance schedule are performed with nothing more than adequate lighting and a bare eyeball. These tasks provide instructions on what to look at and how closely the identified item should be looked at (the level of inspection). Maintenance schedule builders for large aircraft rely on the Air Transport Association of America (ATA) for standards that categorize the levels to which items may be inspected. The same cannot be said for maintenance schedules designed for smaller aircraft. Let's look at some of the ways in which the problem of defining the level of inspection for a task is handled, so that we can determine whether our interpretation of what is expected meets the requirements.
For large transport aircraft, the term most commonly used, by far, for defining the level of inspection required is that of general visual inspection (GVI). Since, after several amendments, the definition for this term has become a long one, it has purposely been formatted (in this article, and not by ATA) so that it can be separated into a set of requirements as follows:
- "A visual examination of an interior or exterior area, installation, or assembly to detect obvious damage, failure or irregularity.
- This level of inspection is made from within touching distance, unless otherwise specified.
- A mirror may be necessary to enhance visual access to all exposed surfaces in the inspection area.
- This level of inspection is made under normally available lighting conditions, such as daylight, hangar lighting, flashlight, or drop-light, and may require removal or opening of access panels or doors.
- Stands, ladders, or platforms may be required to gain proximity to the area being checked."
The problem is to convey a clear, consistent understanding of the GVI requirements through the use of a definition that will be easily remembered when needed. In this case, the most important thing to remember is that the work needs to be done at arms-length, and all surfaces need to be inspected. A more concise way of stating the requirements may help. Therefore, for ease of recollection, an alternative definition may be, "a visual examination of an interior or exterior area, installation, or assembly, made from within touching distance, to detect obvious damage, failure, or irregularity. This inspection level may require the removal or opening of access panels or doors, and is made under adequate lighting conditions (daylight, hangar lighting, flashlight, drop-light)."
In smaller aircraft inspection schedules, the intent of GVIs may be indicated by use of the word "inspect" or "check," and no definition. It is assumed that the technician performing the work will know what to look for. If there is a concern about consistency, sometimes the wording of the task will include details such as, "pay particular attention to..." This approach attempts to assign levels of inspection through additional instruction, rather than through the use of terms and their definitions. The danger with this is that the inspector may concentrate more on the item so identified, instead of equally-important adjacent items. To obtain a consistent level of inspection in the absence of clear instructions demands additional training or supervision, perhaps backed up by a policy shared with those doing the inspections. As a guide, it may be useful to know that the word "inspect" is often used to differentiate from the word "check." Inspection implies an activity that encompasses a number of different requirements (inspection level, scope, access, lighting, verification of security, etc.), while the word "check" frequently concerns visual verification of a small detail only. How these words are used, therefore, becomes important. ATA has the preferred approach-provide a term and a definition to maintain consistency. Anyone faced with the problem of defining the content of an inspection schedule for a smaller aircraft may use terms and definitions that are already established by the industry to ensure clarity and consistency. Where unique requirements exist, new terms and definitions may have to be developed. If this is the case, ensure that the new terms do not accidentally use established definitions, and vice versa (especially if they are ATA terms and definitions)!
Have you ever noticed people, other than your co-workers, around an aircraft, looking in wheel wells and opening all the access panels, and wondered who they were? Did you get very protective of your company's property all of a sudden? You were probably surprised to find these individuals examining an airplane you are responsible for. You may be the aircraft maintenance engineer (AME) who has to attest for the condition of the airplane, and you certainly should be concerned that others have access to it. In this respect, you are putting your own professional reputation on the line, as well as that of the approved maintenance organization (AMO) for which you work. After all, company procedures and policies in the maintenance control manual (MCM) or maintenance policy manual (MPM) have to be followed, and it's your job to ensure that they are.
The Canadian aviation industry is recognized for a high level of maintenance standards. A major contributor to this is the requirement to have an approved maintenance program and a professional calibre of people performing the maintenance. Consequently, when a maintenance crew encounters an unknown person around the aircraft, it is their responsibility to find out who the individual is, and under what authority they are there.
More than likely, the individual is legitimate and will have official credentials to explain their presence. Authorized personnel, such as Border Services Officers (BSO) (formerly called Customs Officers), will be able to show you their official credentials. In order to perform their job effectively, they must have unfettered access to the aircraft. To explain this, it is important to remember that they are working with the best interest of the Canadian public in mind. Their role is to look for hidden narcotics and other such contraband, or smuggled goods that can also jeopardize the safety of the aircraft, due to where they are hidden. Their inspection activities are very much a joint effort with the aviation industry to enhance border security, combat organized crime and terrorism, increase awareness of customs-compliance issues, and help detect and prevent contraband smuggling.
A closer look at their inspection practices highlights how this is accomplished. The CBSA uses a variety of technologies and initiatives to detect contraband and prohibited or restricted goods. They share information from their independent inspections and encourage the industry to do the same. Often, AMEs are faced with a situation where contraband is discovered and is turned over to BSOs. Conversely, BSOs may encounter aircraft components in need of adjustment or repair, and can pass this information along to the maintenance personnel.
Any aircraft on an inbound flight from a foreign departure point may be subject to inspection by customs. The CBSA selects aircraft for inspection based on a risk-management approach, focusing on flights that represent the highest level of risk. When BSOs are going to perform an inspection, they make every effort to notify the aircraft operator in advance, through its dispatch centre. When they perform a ramp inspection, they open exterior access panels that have "quick-release" style fasteners or interior panels with quick-release or screw fasteners. Should the officers wish to open other panels, they are instructed to seek the assistance of an AME. Upon the completion of the BSOs' inspection, the team leader documents their actions, listing any panels that were removed for access, and all areas that were inspected. The inspection report is left with the airline representative or, if no one is available, in the flight deck. With this information available, maintenance staff can verify that everything has been properly secured, or they can reopen the listed panels to look inside for themselves, and close them again for personal satisfaction that there are no mechanical infringements and the maintenance documentation requirements have been met. If an airline or their maintenance organization has concerns about an inspection, they should contact the local CBSA airport office to address them in a timely manner.
CBSA inspectors play a vital role on behalf of the Canadian public. Their officers are well trained and make every effort to work in conjunction with the airlines to ensure their activities do not jeopardize safety.
Occasionally, CBSA activities may cause delays-but not always. In some cases, things such as short turn around times, gate changes, late arrivals, and bad weather can mean it takes them a bit longer than everyone would prefer. Often, BSOs encounter problems in the inspection process, or they actually find something that wasn't supposed to be there. A delay is unfortunate, but they still require time to do their job properly and cautiously.
The CBSA has an important job to perform. There is no argument that their work is valuable, and that their presence on the ramp is a valid element in airline operations. However, in most cases, there is no consideration or leeway in the dispatch process provided to the CBSA to account for this unscheduled ramp activity. That means that, to a certain extent, the CBSA relies on co-operation with the airline to get the aircraft for their inspection, even though they have legislated authority in that respect.
Over the past few years, members of the various airlines, associated maintenance organizations, and the CBSA have been working together to develop standardized procedures for alerting the airlines of a pending inspection, the inspection process, and the paperwork that provides notification of the work and any panels disturbed. This has been a joint effort with complete buy-in by all interested parties. Transport Canada (TC) was involved as a key partner to ensure that the aviation regulations were taken into consideration, and that overall safety was not compromised. The combined process of aircraft inspections promotes "watching together" and "working together" concepts for all parties, and heightens awareness of the intricate systems and co-ordinated efforts required to get all things done, while limiting inconvenience for the average traveller.
On a regular basis, the CBSA discovers and confiscates drugs, arms shipments and contraband commodities. Their activities not only contribute to making Canada safer, but they also enhance aviation safety. They work proactively, at all times of the day and night, to perform their duties. Their work habits parallel those of the AME. So the next time you see a CBSA officer around your aircraft, work with them so they can do their jobs with minimal disruption. To learn more about the CBSA, visit http://www.cbsa-asfc.gc.ca/.
In Aviation Safety Letter (ASL) 1/2007, we referred to two aviation occurrences involving reversed flight controls. The System Safety Office in the Quebec Region studied these two occurrences. Below is an abbreviated and slightly reworded version of the two Transportation Safety Board of Canada (TSB) occurrence reports.
Incorrect assembly of the aileron control system on a Cessna 172L
TSB Occurrence Report No. A00Q0043
The pilot owner of the Cessna 172, was making a visual flight rules (VFR) flight. The aircraft was carrying four persons. When the aircraft was at an altitude of 5 500 ft above seal level (ASL), the right-hand aileron yoke assembly came apart, and the pilot lost lateral control. He immediately declared an emergency on the 121.5 MHz frequency and was guided by the control centre to an airport, where emergency services were standing by. The elevator was functioning normally, but the pilot used it as little as possible for fear that the flight controls might jam completely. He successfully landed at Maniwaki, Que., without incident. No one was injured.
On April 7, 2000, after the annual inspection of his aircraft, the pilot left the airport at about 16:45 Eastern Daylight Time (EDT)1. When the aircraft was 13 NM from the airport, at an altitude of 2 700 ft, the pilot noticed that the aileron control was no longer responding. Using the elevator, its trim tab, and the rudder, the pilot managed to turn back and set the aircraft down on the runway. The landing proceeded without incident, and the pilot did not declare an emergency.
When the pilot arrived at the hangar, the employees had all left the premises except for the maintenance manager. The maintenance manager checked the malfunction and found that the right-hand aileron yoke assembly had come apart and that some parts had fallen to the floor of the aircraft. The pilot's lack of a night rating put additional pressure on the maintenance manager, who rushed to complete the work before it began to turn dark.
He put the universal joint back in place, checked the operation again, and returned the aircraft to service without making any entries in the technical log or asking another person to perform an independent inspection.
The pilot took off again at about 18:25, and the flight proceeded without incident to the airport.
Four days later, the pilot took off again, and the right-hand aileron yoke assembly came apart again. The aileron and the elevator mechanisms are linked; the elevator responded normally, but the left aileron had a tendency to ride up and destabilize the aircraft. For that reason, the pilot used the elevator as little as possible, employing the elevator trim tab and the rudder instead. He landed at Maniwaki, where emergency services were standing by.
An apprentice technician had taken part in the installation of the aileron control system, and the maintenance manager had checked the work.
The work on the yoke involved rotating two identical parts from one side of the flight control to the other. The two mechanisms were similar, but access to the right side was restricted by the presence of the radio equipment and map compartment.
In the first occurrence, the work was simple enough for the maintenance manager to entrust to an apprentice technician with only one year's experience, without constant supervision. The apprentice technician was, however, supervised by an experienced apprentice technician.
During the annual inspection, the maintenance manager had suggested to the aircraft's owner that, for economic reasons, the universal joints be rotated instead of just replacing the left joint.
The work involved sliding the universal joint (part number [P/N] 0411257) into the sprocket (P/N 05117851), then pushing the shaft (P/N 0511788-1) into place and aligning it to install the bolt. The bolt would thus hold all the parts together.
In the second occurrence, the maintenance manager had trouble aligning and inserting the universal joint in the sprocket. To ensure the integrity of the assembly, the manufacturer had added a note specifying that washers (P/N AN960-816L) were to be installed on the shaft to limit the distance between the shaft and the bearing (P/N S100443A) to 0.005 in. (See Figure 1: Aileron control system.) The Cessna 172 maintenance manual contains no specific instructions for removing and installing the universal joints. The manual describes, rather, the procedure for removing and installing the control as a whole.
For a better view of the right-hand installation, the technician could have accessed all the parts by removing the map compartment, but he did not do so. The technician therefore had to work by feel in a more confined space. The universal joint was held in place by the pressure exerted by the nut, even though the nut was not in the right place.
Consequently, the abnormality could not be detected in the ground test of the controls. Removing the map compartment would have simplified the access and would have helped to visually confirm the incorrect assembly. The time required to remove and replace the map compartment was a determining factor in this maintenance operation. The distance between the shaft and the bearing was nearly 0.500 in., whereas it should have been 0.005 in. Even an inspection by touch would have been able to detect this abnormality.
In both occurrences, the work of rotating the universal joints was not recorded in the aircraft journey log or in the technical logs.
The pilot was present during the inspection of his aircraft in both occurrences. He remained in the hangar throughout the work and knew that the two universal joints had undergone maintenance work. Under existing regulations, he could have been asked to take part in the independent inspection following the maintenance work, but he was not. He did, however, perform a preflight check, and all the flight systems were functioning normally.
Figure 1: Aileron control system
1All times are EDT (Coordinated Universal Time[UTC] minus four hours).
Loss of control of a PA28-140 on takeoff
TSB occurrence report No. A01Q0009
A Piper Cherokee PA28-140, with two pilots on board, took off on a VFR flight. During climbout, about 25 ft above ground level (AGL), the aircraft rolled to the left. The pilot flying, who was also the owner of the aircraft, applied right aileron to compensate for the turn, but the aircraft continued to turn left. The other pilot also tried to straighten the aircraft by applying right aileron until the ailerons jammed in the full right position. The aircraft flew over a highway, and the left wing tip struck a snowbank on the side of the highway. The left wing separated at the fuel tank, and the aircraft came to rest in a field on the other side of the highway. The two pilots evacuated the aircraft and were taken to hospital for minor injuries. There was no fire.
Since he had not flown in just over three months, the pilot flying asked a more experienced pilot to accompany him and supervise the flight. The purpose of the flight was to allow the pilot flying to confirm that his aircraft was operating correctly. The weather at the airport was suitable for VFR flight, and the surface winds were calm.
Preliminary examination of the aircraft by the investigator at the airport revealed that the bell cranks were installed backwards. The left wing had separated at the fuel tank, and one could clearly see that the bell cranks were not installed properly. By moving the ailerons from outside the aircraft, it was confirmed that the flight controls moved in the opposite direction.
The checklist used by the pilot provided three opportunities to confirm that the ailerons were functioning properly: the walk-around check, the before-start check, and the before-takeoff check. The pilot had to ensure that the flight controls were operating properly by confirming that the deflection of the control surfaces matched the deflection of the flight controls. The flight controls were reportedly checked during the walk-around check, the engine warm-up, and again during the before-takeoff check.
During these three checks, the two pilots ensured that the flight controls moved freely, but they did not pay particular attention to the directional deflection of the control surfaces. The checklist used by the pilot was the one he used during his pilot training. That checklist indicates that the flight controls must move freely, while the detailed checklist in the manufacturer's flight manual indicates that the flight control surfaces must be checked for proper deflection.
During the annual inspection, the aircraft maintenance engineer (AME) found that the aileron bell crank brackets were cracked and needed to be replaced.
The aircraft owner asked that his aircraft be repaired before the maintenance company closed for the Christmas break. The parts were ordered, and the replacement work began on December 20, 2000. The maintenance company was short one AME and had another aircraft to fix before closing, so the replacement work was completed in a hurry on Friday, December 22, 2000.
Figure 2: Aileron bell cranks on the Piper PA28-140
This task involved removing the two fuel tanks to access the bell crank bracket mounting rivets. The work was laborious because the numerous fuel tank fastening screws were extremely rusted and hard to remove. The work took much longer than usual.
The task consisted of releasing the tension on the aileron cables in order to move the bell cranks into the wing without having to remove them from the aircraft. But because the bell cranks were so greasy, the AME decided to remove them to clean and inspect them.
The two bell cranks were not marked with a part number for identification. It would have been necessary to use the manufacturer's manual or parts manual for a diagram of the bell cranks installation, but this was not done. It was not the first time this task had been done in recent months; the AME had performed this task a few times during the past year.
Most aircraft maintenance shops use a microfiche reader for aircraft maintenance. As a result, the AME must either read the microfiche and memorize the procedure, or go back and forth repeatedly to the reader. Some readers have a feature allowing the microfiches to be printed out; this particular reader did not have a print feature. Consequently, the AME elected to perform the work from memory instead of using the microfiches. As a result, he interchanged the bell cranks when reinstalling them, thereby reversing the aileron controls.
The bell cranks were removed from the wing during reassembly, contrary to normal procedures. Therefore, an additional check-"Installation of aileron bell crank assembly," mentioned in section 5.11 of the maintenance manual-was required. Section 5.11(d) also indicates that aileron deflection must be verified using the method specified in section 5.12. If this check had been performed according to the procedures, the AME would have noticed that the bell cranks were installed backwards.
The AME who performed the work was the company president and director of maintenance. An independent AME recorded the independent inspection in the aircraft technical log; he did not notice that the controls were reversed.
Tests were done on the same model of aircraft to determine whether there was an obvious difference between the two installations that would have alerted an AME performing this maintenance task. Both bell cranks were removed and mounted backwards as on the occurrence aircraft. The installation appeared correct at first glance, except that the fasteners for the aileron control rod, located toward the wing tip, put the rod out of alignment and caused a very slight rubbing against the skin of the trailing portion of the wing. The rubbing was not audible, and there was nothing wrong with the operation of the ailerons, except that the aileron directional deflection was reversed and the range of deflection was changed.
According to the aircraft maintenance manual, the ailerons must be adjusted to deflect upward 30° and downward 15°, with a tolerance of 2°. Bell crank travel is limited by stops on either side. Before the bell cranks were mounted backwards, the aileron deflection during this test was within the limits prescribed by the manufacturer. After the bell cranks were mounted backwards, the left bell crank did not come into contact with the forward stop, and the aileron deflection was not within the prescribed range. The right aileron could deflect upward 18° and downward 14°, and the left aileron could deflect upward 25° and downward 14°.
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