CASS ... Too Little ... Too Late

Oct. 25, 2007
Continuous Analysis and Surveillance FAR 121.373a: No surveillance ... no analysis

FAR 121.373a: “Each certificate holder shall establish and maintain a system for the continuing analysis and surveillance of the performance and effectiveness of its inspection program and the program covering other maintenance, preventive maintenance, and alterations and for the correction of any deficiency in those programs, regardless of whether those programs are carried out by the certificate holder or by another person.”


Several recent air carrier accidents, one in particular, focused attention on the FAA mandated Continuing Analysis and Surveillance System, (CASS) which all air carriers (FAR 121 and 135 with more than 10 seats) have been required to follow for more than 30 years.

Little attention was paid to the FAR, and in too many cases, it was simply ignored as too complex, time consuming, and or of little use. There appeared to be little surveillance or enforcement even though a monthly report is supposed to be filed with the FAA and some carriers had been cited through the years for failing to implement such a program. At times, even where they did, they did not follow their own approved surveillance program. Violations and fines against the carriers became an added threat against chief inspectors, directors of maintenance, and various company executives through the years, especially where data was false and or intentionally falsified.



We all remember the tragic loss of the ValuJet (now AirTran) DC9 in May of 1996 in the Florida Everglades. It was brought down because of a fire that started in a cargo compartment ignited by improperly stored oxygen canisters. This accident marked the start of a significant change in the FAA’s attitude toward enforcement and terminated the kinder and gentler era of David Hinson. (FAA Administrator). Enforcement was ramped up and the pressure was on maintenance in the air carrier business.

However, there was no significant focus on continuing analysis and surveillance during the investigation and congressional hearings simply because there was no clear maintenance failure regarding the accident. The oxygen canisters were being shipped to another station for re-certification and were not given the special handling they deserved. The accident was partly due to untrained workers who failed to handle and store the canisters with the care required of hazardous items.

But continuing analysis and surveillance does apply generally to inspection and performance of maintenance activities. Removal, inspection, packing and shipping of oxygen canisters is a continuing airworthiness maintenance and inspection function and hazmat handling should be included within the surveillance activities of an air carrier’s CAS committee. Since their replacement was required on a regular schedule it would be logical to have this item noted during CAS and perhaps focus attention on the extreme care required in their handling. The regular nature of the inspection of these canisters should have placed their surveillance under the CASS scrutiny and just maybe could have prevented the accident. The CASS did not work for this accident.

Alaska Airlines

A few years later the accident that changed everything regarding enforcement of FAR 121.373 was the Alaska Airlines crash where the MD80 horizontal stabilizer trim drive was defective and caused the aircraft to impact the ocean just north of Los Angeles. Clearly, a maintenance deficiency and clearly within the surveillance requirements of CASS.

When the inspectors converged on Alaska Airlines they focused their attention on the Alaska CAS program and found that it just did not exist or simply was not implemented. The problem with the trim drive was a particularly sensitive one and was a recurring wear problem that the airline should have included in its CASS. Here again the CASS did not work.

The CAS program was important in that it might have detected the recurring trim drive wear problem early on and focused more attention on it. The cause of the accident was found to be a negligently maintained stab trim drive. There was a lack of proper lubrication and excessive wear on the acme threaded drive mechanism. The FAA and the NTSB opined that a properly functioning CAS system might have detected the dangerous nature of this fault before the accident occurred. (It’s interesting to note that the J3 Cub I flew many years ago has a similar acme threaded hand crank operated stabilizer trim mechanism.)

Needless to say, there was an order for all inspectors to pay special attention to FAR 121.373. The FAA further ordered a special inspection of 25 major airlines to determine the state of their CAS programs. The results of these special inspections were so controversial that the FAA refused to release them for almost two years. The CASS became a primary focus of FAA inspectors assigned to air carriers. At last, some attention.

Chalks Ocean Airlines

A few years later in December 2005, a Chalks Airlines turboprop Grumman Mallard lost a wing shortly after it took off and crashed near Miami, FL. Structural failure of the wing was cited as the obvious cause.

The NTSB found that “…Chalks maintenance program and practices were deficient, and these deficiencies were causal to the accident.” Again, another clearly continuing maintenance analysis application.

Chalks was an FAR 121 air carrier and did have an FAR 121.343 CAS program set out and described in its maintenance manual. The program was an approved maintenance program that included a quality control function that, in accord with the regulation, is designed to continuously monitor the program and catalog maintenance discrepancies. The conclusion by the accident board was that the system just did not work and that it did not track discrepancies. The Board said that both maintenance and oversight (surveillance by both the company and the FAA) was not adequate.

The Board elaborated by saying that the wing separation was a result of the failure of Chalks maintenance program to identify and properly repair fatigue cracks in the wing, and the failure of the FAA to detect and correct deficiencies in Chalks maintenance program.

Here again, an FAR mandated inspection and analysis system did not work. Although the Board in its report was kind to both the operator and the FAA personnel when it stated further that the FAA’s mandate was a “one-size-fits-all” approach that should be expanded to add more detail in just what the carriers should address. The Board went on to say that the inspectors’ guidance from the FAA did not account for specific risk factors (saltwater for Chalks).

The so-called “risk factors” were all too evident! 1. Older aircraft, (most of the Mallards were built in 1947) although re-engined with PT-6’s in recent years. 2. Saltwater an all too obvious risk factor for corrosion and deterioration of structural components. This writer started flying in Luscombe 8F and Piper PA 18 floatplanes. Saltwater corrosion was an all too obvious risk and very evident. We were required to wash down all aircraft after flight with fresh water when returned to the ramp. Nonetheless, you could frequently find spots under the aluminum wing of a Luscombe where you could poke a pencil through the corroded aluminum skin. The spars were frequently looked at and protected with anti-corrosion liquids as far as could be done with the wings in place. Wing skins were frequently replaced. The fabric surfaces of the PA 18 faired much better in this regard although other steel parts bore the brunt of corrosion from saltwater. Engine parts faired little better. Exhaust manifolds, frequently leaked. There is no let-up to saltwater corrosion. All you can do is slow it down.

Chalks Mallards wings had integral fuel tanks. Any fuel leak meant that the integrity of the wing could be compromised in the area of the leak. Every fuel leak does not mean a structural problem but they must be cataloged and of course sealed and inspected where necessary. The Board urged that all leaks and other structural deficiencies should have been tracked carefully by Chalks. Here again, the CASS failed.

Modern airliners have integral fuel tanks in the wings. The sealing methods and material however are probably much improved since 1947 when the Mallards were built. Even the Convair series of piston and turbines (240, 340, 440, 580, 5800) are all wet wings with integral fuel tanks. They are prone to wing fuel leaks as well. The Convairs were built like battleships, that’s why many still fly today. Most are not of course exposed to saltwater.

Changes need to be made

In order to be effective FAR 121.343 needs to be expanded. The NTSB in Chalks mentioned that the CASS is a “one-size-fits-all” rule. The Board specifically said that the FAA should move away from the one-size-fits-all language of FAR 121.343 and focus on a program that will more aggressively uncover and address any structural and or other continuing airworthiness issues.

A vigorous maintenance discrepancy tracking process must be included in the overall quality control system. The Board also cited insufficient FAA oversight. Principal maintenance inspectors should be required to attend and participate in all regular CASS committee meetings and join in the analysis of discrepancies and maintenance and inspection functions. The Board wants more oversight, this would be a quick start. The following recent change is a start at the assessment stage of inspection.

Recent changes, revisions to Order 8300.10

FAA Notice N8900.7, Revision to Order 8300.10, Volume 2, Chapter 65, and Volume 3, Chapter 37 now provides additional guidance to all principal inspectors and all other assigned aviation safety inspectors on revisions to FAA Order 8300.10. The Airworthiness Inspector’s Handbook,” Volume 2, Chapter 65, Assess Section 121.373 or 135.431, the “Air Carrier Continuing Analysis and Surveillance System,” which has been completely re-written, and cancels Volume 3, Chapter 37, “Monitor Continuance Analysis and Surveillance Program/Revision.”

The changes described in the inspector’s assessment of a carrier’s CASS have been expanded and made more detailed in order to focus more attention to more vigorous continuous assessment of the system.

These changes are an important step toward the refinement of CASS requirements under 121.373. But is it enough?

Safety data collection

FAA has numerous reporting systems (perhaps too many) in place today but only one is required by regulation. That is 121.373. When you look at all the reporting activities now in place one wonders what happens to all the collected information and does it achieve the desired objective?

ATOS, the Air Transportation Oversight System, is designed to be somewhat like the CASS in that it is a continuous but broader program designed to detect weakness and predict an accident before it happens. This is what the CASS is supposed to do, but has failed in too many cases. ATOS uses a systemic approach by attempting to evaluate all the elements of the air carrier’s operating environment and it is supposed to ensure that all the elements have safety built into their operating systems. But, this is a much broader look at the whole airline operation than the CASS. ATOS has yet to be fully implemented and fails to include all air carriers. Perhaps CASS should be merged into ATOS so that a uniform approach can be applied.

FOQA, Flight Operational Quality Assurance, is a far-reaching attempt by the FAA to capture flight data and other operational information. The stated purpose is to (again) focus on problems before they cause an accident. There are many concerns about the collection and use of this data from the pilots unions and of course their use in civil litigation. FOQA operates as a voluntary participation program.

ASAP, the Aviation Safety Action Partnership, is another voluntary data sharing program that has been around for awhile but shares the same concerns that all the data collection systems share … how will the data be used? Most carriers are reluctant to share raw data without adequate protections from disclosure. Of course the raw data of maintenance discrepancies are provided through the CASS. Many would suggest that many of the programs should be combined or eliminated altogether.

Aside from the above data collection activities there are others: Cockpit Voice Recorder Data, Flight Recorder Data, Self-Disclosure Data Program (AC00-58), and the Aviation Safety Reporting System.

CASS needs further improvements. Send your comments to [email protected].