Thursday, December 31, 2015

How is it Possible to Land an Airliner on a Taxiway?

Alaska Airlines 737 departing from SeaTac

An Alaska Airlines 737 landed on a taxiway at Seattle's SeaTac airport on December 19th at about 8:30 in the morning. While it is not unknown for this sort of thing to happen, it is thankfully rare but also exceedingly dangerous. Luckily for this crew and their passengers, the taxiway was clear at the time and the landing was uneventful.

Taking off or landing on the wrong piece of pavement has been the cause of a number of incidents and accidents over the years. One of the most deadly in recent memory was the crash of a Singapore Airlines 747 which attempted to take off on a closed runway back in 2000 in Tapei and impacted parked construction equipment killing 76.

Another deadly incident was that of Comair 5191 whose pilots mistook a shorter runway for the one they had been cleared to use resulting in an overrun accident and 49 fatalities.

Wrong runway and wrong airport landings also occur but on occasion lady luck smiles on the errant pilots. A Southwest Airlines 737 enroute to Branson, Mo. landed at a small general aviation airport several miles short of its intended destination last year. Quickly realizing their mistake, the pilots were able to stop the plane on the very short runway thereby averting a serious accident.

I even recall an incident from many years ago when an American Airlines plane landed at Biggs Army Airfield instead of El Paso Intl, which was its destination. The two airports are immediately adjacent to one another. I remember this incident because not long after that, I had a student pilot of mine attempt to land at El Paso while our destination was Biggs.

As you can see, wrong runway errors are committed by both inexperienced pilots as well as seasoned aviators.

So with the possibility for such deadly results, how is it that pilots can take off or land on the wrong runway or a taxiway? The answer is that it is not easy to do this but it is easier than you might think. And there is a common factor in all of these incidents and accidents. That factor is complacency.

How Could This Happen?

Alaska Flight 27, a Boeing 737-900, arrived in the Seattle area from Chicago at about 08:15 AM and was vectored by Seattle Approach Control to an ILS approach to runway 16 Right. SeaTac has three parallel runways labeled 16 Left, Center and Right. The "16" denotes the approximate runway heading of 160 degrees (it's actually 163 degrees). There is also a taxiway named "T" or Tango, running parallel to the runways between the center and right runway.

An ILS is a ground based radio guided approach which provides both vertical and horizontal guidance to the pilots. When flying this approach, the pilots would be presented with precise lateral course information. Deviation from the course or a lineup on the wrong runway would be prominently displayed on the instruments. 

For this reason, pilots are encouraged or required to always have ILS information tuned in and displayed even when flying a visual approach. And speaking of which, the weather at the time of the incident was quite good:

KSEA 191637Z 12010KT 10SM SCT022 03/02 A2991 RMK AO2 $
KSEA 191553Z 16007KT 10SM FEW016 BKN025 03/02 A2990 RMK AO2 SLP134 T00280017 $ 

This translates to a thin ceiling at 2500 feet at the top of the hour and no ceiling in the report at the bottom of the hour with the visibility being very good. Clearly weather was not a factor and the aircraft was cleared for an instrument approach to the outside runway. How then did they end up on the taxiway?

Cleared to Sidestep

Just a few minutes before landing, and after the aircraft had switched from Seattle Approach Control to Seattle Tower, the tower controller asked if they'd like to land on the center runway. The aircraft stated that they would like to switch runways and were subsequently cleared to land on runway 16 Center.

This maneuver is called a "sidestep" and is a visual maneuver, meaning that it is accomplished using visual and not instrument cues. A tower controller may offer a different runway to a landing aircraft for a number of reasons such as tight spacing on a preceding aircraft, or perhaps a desire to get an airplane with a flow time airborne. In this case, it appears as if the tower controller was simply doing a favor for the Alaska jet as the taxi time from the closer runway would be shorter. 

The audio from the tower frequency can be heard here. The clearance for the sidestep can be heard at the 28:00 minute point.

So at this point, the aircraft accepted the sidestep clearance and would start maneuvering visually to land on the center runway. What else might have affected the crew's ability to identify the correct runway?

It's hard to say for sure but there are some clues. For one, the center runway has just been completely rebuilt. The new pavement on the freshly rebuilt runway is still most likely clean and lacking the usual rubber deposits that most runways have.

Another consideration would be the angle of the sun. The aircraft touched down at 8:31 AM and sunrise in Seattle that morning was at 7:58 AM. The angle of their approach would have put the sun almost directly in their eyes further obscuring the markings on the taxiway as seen in the graphic below. This would have been made worse as they attempted to maneuver to the left of course to line up on the center runway.

The sun was likely obscuring the pilot's vision
The orange line shows the sun direction at 0831 on Dec 19th

How Could This have been Prevented?

One of the more challenging aspects of aviation is that seemingly routine or innocuous situations may contain hidden danger. And there will rarely be obvious signs pointing out these pitfalls. This is why it is incumbent upon pilots to maintain vigilance during not only difficult weather, but also during a simple visual approach in good weather. Some might say especially during good weather.

Being able to recognize when conditions are subtly changing while having the appearance of normalcy is a core skill used to battle complacency.

Another technique that could have been used would have been to have the non-flying pilot tune in the frequency of the approach to the new runway. Often this can seem redundant if the landing runway is in sight, but this crew is probably now wishing that they had. 

What Happens Next?

There will be an investigation. The FAA has already said that they are looking into the event. The pilots will most likely not be fired but they may face some discipline in the terms of time off from work which means lost income. They will also likely have some retraining or a checkride before flying again.

The pilots may, however, not face any punitive action at all if this event is accepted into a safety reporting program. In these industry-labor-regulator partnerships, mistakes made in good faith can be provided immunity from sanction to enhance the reporting of safety related information.

The hazard that this taxiway presents has already been noted in a warning printed on the airport layout depiction as seen below. That this hazard was known may even mitigate in the pilot's favor. 

A warning about taxiway T is printed on the Seatac airport profile

We can probably expect to see some new measures such as large letters painted on the taxiway and further warnings designed to prevent this from happening again but nothing is as effective as maintaining a watch against complacency.

Wednesday, December 09, 2015

Shifting Currents: Will Regional Airlines Survive?

Regional airlines are operated by little known third party airlines.

It would  appear to observers of the domestic US airline industry that things are finally settling down. After years of turmoil, bankruptcy and consolidation, the remaining big four US major airlines control nearly three quarters of all domestic airline seats. Low fuel prices have meant a season of record profits as well.

The regional airline market, however, is a somewhat different story. Whipsaw fuel pricing, the introduction of a new class of small jets and a pilot labor shortage along with a reassessment of the relationships between regionals and their mainline partners could be changing the landscape.

The regional airline business model consists mainly of little known companies such as Envoy, Expressjet or Republic Airlines that fly airplanes in their major airline partners' livery. Flying as American Eagle, United Express or Delta Connection, these companies sign "capacity purchase agreements" with their major partner airlines to provide service between major airline hubs and smaller regional airports that don't support a mainline aircraft.

Regional Airlines: How We Got Here

The industry has always existed to ferry passengers from major hubs to small feeder cities, but the introduction of small regional jets from the late 1990s fundamentally changed the dynamics of the business model. These small jets such as the 50 seat Bombardier CRJ 200 and the Embraer ERJ 145 could not only go as high and as fast as their major airline brethren, but could also and more importantly, fly as far.

What this meant is that regional airlines could poach passengers from each other's regional feeder airports. For instance, historically, to fly out of a regional airport such as Twin Falls, Idaho, one would have to take a regional airline to the nearest hub which was within the range of the smaller and slower turboprop aircraft. This probably would have been Salt Lake City where Delta was the dominant major airline. The new regional jets (RJs) allowed regional airlines to now fly directly from a smaller city to a hub in another region such as LA, or Chicago.

It also meant that regional airlines were no longer strictly feeders to their mainline partners but rather operators of parallel airlines under the same corporate identity. The real brilliance of the arrangement, however, was that the regional partners were not covered under the collective bargaining agreements which kept labor costs high at the mainline network airlines. How did this happen?

The Unions Get Snookered

The one aspect of collective bargaining agreements (CBAs) that unions are most jealous of is their scope clause. A scope clause will delineate which work must be accomplished by employees covered under the CBA and which work, if any, can be outsourced. Obviously unions have an interest in keeping the most work in-house and under the agreement.

In fact, unions view scope clause protections as so vital, that those protections are usually set forth in the first section of many airline labor contracts. Thus, the term "Section 1" protections becomes a shorthand for all the restrictions on who may perform work for the company with which the union collectively bargains.

It was a lack of imagination and vision on the part of mainline union negotiators that allowed both existing provisions for the outsourcing of regional flying to remain in airline CBAs, or for those provisions to be imposed after the wave of post 9/11 airline bankruptcies. Mainline union negotiators were caught flat footed by the introduction of the new capable RJs which resulted in stagnation in the amount of flying they controlled. They simply didn't think that the provisions for commuter aircraft flying in their contracts would eviscerate their members' livelihoods.

In 2000, for instance, regional airlines flew a total of 24 billion revenue passenger miles (RPMs), but by 2010 that number had increased three fold to about 75B RPMs. In the same time frame, all network mainline airlines flying stagnated at about 360B RPMs until 2007 followed by an erosion to about 320B RPMs in 2014. The data can be found here and here.

Some, but not all of this mainline stagnation could be attributed to the growth of low cost carriers (LCCs) like Jetblue, Southwest and AirTran airlines, but it became clear that regional airlines were doing a fair bit of the flying that mainline airlines might have done themselves.

In 2011 for instance, regional carriers accounted for 64% of all departures at Chicago's O'Hare airport and 74% at Seatac. Some city pairs such as Nashville - Chicago (O'Hare) have had only RJ service while others such as Austin - Denver might have a mix of RJs and mainline aircraft. Three of the largest regional airlines, Envoy, ExpressJet and SkyWest can be even now counted as major airlines in their own right with each having over a billion dollars of annual revenue.

Alter Egos

What one should be careful to not do, though, is to assume that mainline carriers are in actual competition for business with their regional partners. This is due to the nature of the capacity purchase agreements (CPAs) that mainline and regional airlines have entered into. In a capacity purchase agreement, the mainline carrier simply purchases all the seats on the regional aircraft while retaining the marketing, ticketing, and most importantly, the revenue from the sale of tickets.

The regional carrier gets paid regardless of how many seats are filled or how the customer is ultimately treated. The regional airline is effectively wet-leasing its aircraft to the mainline. You can easily see how incentives line up for a less than optimal customer experience on regional airlines...they're getting paid either way. The lack of amenities, spartan service and cramped cabins have made regional jets increasingly unpopular with the traveling public.

So if the customer experience is so negative, why do the mainline airlines outsource their valuable branding and operations to third parties who get paid regardless of product quality? Cost control. Salaries are notoriously low at regional airlines with some crew members qualifying for food stamps. In fact, due to the long term contracts regionals have with their mainline partners, the only way for a regional airline to increase unit revenue is through cost control and cost reduction, which is exactly what they've done and become very good at.

So who wants to work at such a place? One of the reasons that employees may accept the low wages offered by regionals is that hiring standards are lower, or perhaps employees hope to gain needed experience in the industry in hope of landing a better job at a major airline.

This is especially true for aspiring pilots who can count their flight hours as a form of pay. Most mainline airlines have minimum hours requirements for pilots to be considered for hiring. The only way for a young pilot to get this experience other than joining the military has traditionally been to fly for a regional airline. New federal regulations, however, are changing that dynamic which I wrote about here.

The arrangement between regionals and mainline carriers has many of the usual suspects and social justice warriors in a degree of moral high dudgeon due to low wages, but my view is somewhat moderated. It's simply not true that forcing wages higher will result in a greater quality product while leaving service distribution unchanged. In many cases, smaller cities will just lose scheduled air service as costs climb. This is already happening.

Flies in the Ointment

The regional industry has several other vulnerabilities which may eventually change how they do business. One particular achilles heel is the high seat-mile cost that the small jets have. While the cost to acquire and operate a 50 seat jet is only marginally less than say a 737, a 737 will have nearly three times the seats and therefore three times the ability to generate revenue.

After huge fuel price spikes in the late 2000s it became apparent that the economics of the 50 seat jets didn't really work. As a result, many of those jets are being traded in for the larger 70 and 90 seat versions. A new generation of small jet such as the Embraer E series and Bombardier C series of jets feature larger cabins, first class seating and are as comfortable as mainline Boeings or Airbuses.

Now though, with the larger capacity aircraft, regional airlines are bumping back into union contracts which restrict the outsourcing of aircraft of larger than 90 seats. Coupled with an ongoing pilot shortage, at least two mainline carriers, Delta and United, have considered bringing their regional airline operations back in-house.

Bringing the Flying Home?

Last summer, Delta proposed to their pilots a purchase of 20 Embraer E-190 regional aircraft and United recently approached their pilot union with an offer of increased pay which included the introduction of either the Embraer or Bombardier 100 seat aircraft. While Delta pilots turned their offer down for unrelated issues, pilots at United have yet to vote on the new pact which also includes pay increases.

It seems apparent that with the pilot shortage driving higher pilot salaries, the advantages of outsourcing regional aircraft flying to a third party where customer service may suffer is being outweighed by keeping the flying in-house.

Friday, December 04, 2015

Should Airplanes Be Flying Themselves?

For anyone interested in going deeper down the rabbit hole of the problems of automation and the concurrent (and inevitable) deterioration of piloting skills, William Langewiesche wrote a great long-form recount of the crash and investigation of Air France 447:

 For Flight 447, it was too late: the probes were quickly clogged. Just after 11:10 P.M., as a result of the blockage, all three of the cockpit’s airspeed indications failed, dropping to impossibly low values. Also as a result of the blockage, the indications of altitude blipped down by an unimportant 360 feet. Neither pilot had time to notice these readings before the autopilot, reacting to the loss of valid airspeed data, disengaged from the control system and sounded the first of many alarms—an electronic “cavalry charge.” For similar reasons, the automatic throttles shifted modes, locking onto the current thrust, and the fly-by-wire control system, which needs airspeed data to function at full capacity, reconfigured itself from Normal Law into a reduced regime called Alternate Law, which eliminated stall protection and changed the nature of roll control so that in this one sense the A330 now handled like a conventional airplane. All of this was necessary, minimal, and a logical response by the machine. 
So here is the picture at that moment: the airplane was in steady-state cruise, pointing straight ahead without pitching up or down, and with the power set perfectly to deliver a tranquil .80 Mach. The turbulence was so light that one could have walked the aisles—though perhaps a bit unsteadily. Aside from a minor blip in altitude indication, the only significant failure was the indication of airspeed—but the airspeed itself was unaffected. No crisis existed. The episode should have been a non-event, and one that would not last long. The airplane was in the control of the pilots, and if they had done nothing, they would have done all they needed to do.

It's a great article. Read the rest here.

Thursday, December 03, 2015

Air Asia 8501: The Automation Failed First Followed by the Pilots

Automation failure caught the pilots by suprise

The final report on the crash of Air Asia 8501 was released on December 1st and serves to highlight a number of problems with highly automated aircraft and the pilots who fly them. If you'll recall, this was an A320 which crashed into the Java Sea killing all 162 passengers and crew last December.

In short, a broken solder joint had caused multiple fault indications in a rudder control unit during the flight. By itself this was not a huge problem, but when the captain attempted to reset some circuit breakers in response, the autopilot disengaged and the underlying rudder fault became a problem.

From the accident report:

The cracking of a solder joint of both channel A and B resulted in loss of electrical continuity and led to RTLU (rudder travel limiter unit) failure. The existing maintenance data analysis led to unresolved repetitive faults occurring with shorter intervals. The same fault occurred 4 times during the flight.  
The flight crew action to the first 3 faults in accordance with the ECAM messages. Following the fourth fault, the FDR recorded different signatures that were similar to the FAC CBs (circuit breakers) being reset resulting in electrical interruption to the FACs. 
The electrical interruption to the FAC caused the autopilot to disengage and the flight control logic to change from Normal Law to Alternate Law, the rudder deflecting 2° to the left resulting the aircraft rolling up to 54° angle of bank. 
Subsequent flight crew action leading to inability to control the aircraft in the Alternate Law resulted in the aircraft departing from the normal flight envelope and entering prolonged stall condition that was beyond the capability of the flight crew to recover.

So this crew was confronted with a technical issue which had recurred numerous times. It appears that the captain became frustrated with the repeated messages being generated by the faulty rudder unit and finally pulled the FAC circuit breakers. His goal was to reset the computers which he'd seen a maintenance technician do on the ground. It's an understandable impulse, and one that many users of computers have felt: if it's acting wonky, just reboot it.

It should also be noted that this procedure was unauthorized for the situation. The "electronic centralized aircraft monitor"or ECAM, is a display which alerts pilots if something goes wrong and also provides checklist steps to resolve the issue. Pulling circuit breakers is almost never called for and wasn't the correct procedure here. The captain got ticked at having to address the recurring issue and went off the script to apply his own "fix" by recycling the FAC circuit breakers.

The problem was that in resetting the computers, he was in effect sawing off the branch upon which he was sitting. To understand why, we need a little background on the airplane and its flight control systems. The highly automated Airbus has no direct mechanical linkage between the cockpit and the wings, but is rather controlled by a total of seven computers including two flight augmentation computers or FACs. These computers control the movement of the control surfaces using input from the pilots.

Alternate Law

The computers normally provide protection from unsafe flight regimes such as a stall or upset. However, when the computers sense that there is something wrong with their inputs, they revert to a mode known as "Alternate Law" where the computers no longer provide such protections. Pulling the circuit breakers, or essentially cutting power to the computers caused them to revert to alternate law.

It is here where the real problems began. In control of the aircraft at that time was the relatively inexperienced first officer who had just over 2000 hours total time. After the aircraft reverted to alternate law, the rudder malfunction manifested itself in a deflection of the rudder.

A deflected rudder at altitude can quickly upset a swept-wing transport like the A320 due to an aerodynamic phenomenon known as "roll coupling". This is where a yaw input, or movement about the vertical axis, induces a roll. It is an artifact of the swept-wing design of modern airliners and normally not a problem. Here it became a big problem.

Stall Warning

The aircraft immediately rolled to the left at a rapid rate and yet the first officer did not apply any stick input for 9 seconds, which is an eternity when your airplane is rolling over. This may have been due in part to the "startle effect" where a rapid and unexpected change takes some time to recover from or to "regain one's wits". Another possibility is that the first officer was not looking at the primary flight display but had his attention on the autopilot which had disengaged.

One of the primary rules of aviation is to "fly the airplane first", but after the relatively low workload of cruise, having to take manual control of the airplane can be disconcerting. Add to this the aural warnings of a disconnected autopilot and a rapid roll and there is little doubt that the first officer had his eggs scrambled at that point.

He did, however, manage to right the aircraft to a nearly normal bank. It was at this time, while the pilots were in manual control of the aircraft and without computer protection, that they killed themselves.

After the aircraft again rolled left, the first officer's side stick input was a sharp pull. This caused the rapid climb rate followed by a loss of airspeed and a stall. The data recorder showed input from the left side or captain's stick about 30 seconds after the initial roll but confusion on the part of the captain and apparent panic on the part of the first officer doomed the aircraft.

A very inexperienced copilot in an automated cockpit.
He had just over 2000 hours total time.
After the abrupt climb and stall, the captain instructed the first officer to "pull down" which is a rather confusing command. Pulling means that the nose will go up, not down. The first officer's reaction was to pull even harder on his stick which is the exactly wrong thing to do in a stall. The nose needed to be lowered so the airplane could regain flying airspeed. At the very least the first officer should have asked the captain what he meant, but in any event any aviator worth his salt knows that control forces must be relaxed, and angle of attack must be reduced in a stall. It's aviation 101. Or should be. 

Dual Input

It was also here that the electronic controls on the Airbus contributed to the problem. Unlike a Boeing which has a two control wheels which are connected mechanically, the side sticks on the Airbus can each provide separate, and opposite, instructions to the flight computers. The aircraft doesn't give priority to either pilot's inputs but rather sums the inputs for a resultant signal. So while the captain was making appropriate inputs to recover from the stall, the first officer maintained his hard pull which resulted in a net nose up command to the flight computers.

Another basic axiom of aviation is that only one pilot flies at a time, and it should always be clear who is in control of the aircraft. The captain failed here by not verbalizing his assumption of control to his copilot. A firmly annunciated "I have the aircraft" should have resulted in the first officer releasing his grip to allow the captain to recover from the stall. That never happened.

This is almost the exact scenario which doomed Air France 447 which I wrote about here. In that accident, a minor upset at altitude was exacerbated by one of the pilots maintaining a backwards pull on his side stick which didn't allow the recovery from a stall. Everyone perished in that crash.

Automation as Blessing...and Curse

A common theme on this blog has been that while the introduction and use of automation on airliners has been an overall boon to both safety and economics, it is not now, nor for the foreseeable future, going to be a replacement for having well qualified pilots who can actually fly airplanes.

That day will arrive eventually, but current technology simply can't yet replicate the required safety margins required to carry passengers.  

Automation has been widely deployed around the world by airlines which operate in countries that lack any significant general aviation or military aviation programs from which to draw pilots. Without these so-called "farm leagues" to train and groom pilots, the trend has been to take very inexperienced pilots with a bare minimum of flight time and to place them into highly automated cockpits. It is there that they will be expected to gain experience before moving into the left seat.

The problem is that highly automated cockpits offer virtually no real experience in real stick and rudder flying. The job consists of managing checklists and systems which the first officer on Air Asia 8501 no doubt accomplished adequately. He just couldn't fly the airplane out of a stall.

An old aphorism states that you can't tell who's swimming naked until the tide goes out. Don't get caught with a naked pilot.