Aviation Safety Letter 2/2003
In-flight Break-up — Can It Happen to Me?
A sudden and catastrophic airframe failure is an event which some pilots may call an act of God, particularly if all operational limits are adhered to, and the aircraft is properly maintained and certified airworthy. However, there usually is a scientific explanation for any such event, which means we can prevent it. Granted, catastrophic airframe failures (because they rarely end up any other way) are rare, but when they do happen, they are likely associated with one or more of the following situations: violent manoeuvre induced by the pilot (excessive "G" force imposed on a wing or tail, etc.), violent manoeuvre caused by environmental conditions (wind gust, turbulence), pilot-induced overspeed, improper maintenance or maintenance error, improper assembly, and last but not least, material fatigue.
The good news is that we can control all of these situations, especially when taken individually. The not-so-good news is that if you combine any two or more, you are looking for trouble. For example, if you fly at or near maximum gross weight and you willingly impose a violent load on your flight control surfaces, you may be auditioning for a Darwin Award. If you don't break the airplane on your first try, you may end up stalling and getting results on your second one.
While certified aircraft are designed to maintain their structural integrity above the limits imposed in the flight manual, flying at or near the certified maximum gross weight should cause you to think twice before yanking the controls around. The airframe will let you know when you jostle the controls at those weights (it is very likely that most of you have experienced such jarring rides in the past). So, a word to the wise, if you're flying near the top end of the envelope, take it easy on the controls.
Certain types of operations put a lot more stress on aircraft than others, such as aerial firefighting, heli-logging, crop-spraying and multi-cycle operations of aircraft, which fly many short trips all day long, in all kinds of conditions of weight and weather. A recent issue of Air Safety Week (ASW) (Dec. 9, 2002) was almost entirely dedicated to the safety record of firefighting aircraft and associated regulations in the United States. It followed the release of the "Aerial Firefighting Blue Ribbon Panel," which had a mandate to assess the safety of federal aerial firefighting. This panel was established after two firefighting fixed-wing airplanes crashed when their wings broke off in flight in the summer of 2002. Both accidents were videotaped and broadcast on national television.
The report highlighted several areas, including (but not limited to) increased demand on an aging fleet of aircraft, accelerated wear (the report says that in terms of structural stresses, one firefighting flight-hour is equivalent to seven "normal" flight-hours), a deplorable safety record for aircraft and helicopters used in fire management, cultural complacency and contractual cost-cutting. On "cultural complacency," the report states, "The [belief] that funding is never sufficient has bred a culture that accommodates risk.an admirable but hazardous 'can-do' ethos that pervades firefighting aviation."
While the Blue Ribbon Panel Report gave praise to the Canadian certification criteria for aerial firefighting aircraft for going "well beyond" the requirements south of the border, these 2002 summer accidents should remind our operators of the inherent dangers associated with this demanding type of operation, and the need to adjust the maintenance accordingly. For pilots involved in such operations, it makes sense to learn as much as possible about those requirements. (For more on the Aerial Firefighting Blue Ribbon Panel, visit: http://www.nifc.gov/aviation/av_blribbon.html.)
What can pilots do about airworthiness and metal fatigue?
Pilots are usually unable to detect underlying metal fatigue or airworthiness flaws visually. However, it pays huge dividends to learn more about your aircraft and about your maintenance team. Pilots who ask their maintenance staff questions tend to be more knowledgeable about the aircraft and can develop a better feel for the overall airworthiness of the aircraft. As perplexing as it may seem to some, many pilots do not scrutinize the journey log book, and even when they do, they rarely enquire about unusual entries.
The most critical requirement for pilots in this area is the obligation to report any airframe overload or overstress they caused, such as a high-G manoeuvre, a hard landing or if any operational limit is exceeded. If a pilot wilfully fails to disclose a "small" deviation in order to avoid retribution, it could develop into an airframe failure down the road. We all want to believe this kind of conduct does not exist within our ranks, but very few could state with certainty that it never happens.
What can we add about the pre-flight inspection that you don't already know? Learn more about the work done recently on the aircraft, and improve your ability to inspect the airframe. Ask an aircraft maintenance engineer (AME) to do a full walk-around with you for the sole purpose of learning more. You will all recall the Bell 206 accident in Beloeil, QC, when the main rotor mast nut had been removed for maintenance and the pilot had to do a quick flight to test another unrelated system. To make a long story short, all defences - which could have stopped the inevitable - failed, and the mast nut was not inspected visually, as it should be when performing a pre-flight inspection on a Jet Ranger. Unfortunately, the main rotor stayed in place long enough during the start to allow a hover and a takeoff, but it soon departed and the helicopter broke apart in flight, killing both occupants. While this is not related to metal fatigue, it was still sudden and catastrophic.
Stick to the limits!
Staying within the operational limits prescribed in the flight operation manual remains the ultimate prevention tool. A few years ago we experienced a series of wing failures on ultralight aircraft; some of the failures were attributed to overload on flight control surfaces or improper assembly. If you elect to fly a non-certified aircraft, or if you are building your own (and there are many of you who do), take the necessary steps to ensure your aircraft will give you maximal structural integrity. Transport Canada and the Canadian Owners and Pilots Association (COPA) are two of the best resources you should draw on when operating non-certified aircraft.
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