June 2015 Issue

TWA514’s Legacy

The NTSB’s probable cause determination: “[T]he crew’s decision to descend to 1800 feet before the aircraft had reached the approach segment where that minimum altitude applied. The crew’s decision to descend was a result of inadequacies and lack of clarity in the air traffic control procedures which led to a misunderstanding on the part of the pilots and of the controllers regarding each other’s responsibilities during operations in terminal areas under instrument meteorological conditions. Nevertheless, the examination of the plan view of the approach chart should have disclosed to the captain that a minimum altitude of 1800 feet was not a safe altitude.”

When You’re Hot, You’re Hot

“Hot spots” are locations on an airport with a history of collision risk or runway incursion. Increased attention from pilots is necessary to safely negotiate them. The excerpted airport diagram at right presents an example of how hot spots are charted. (We changed the color for greater contrast.)

According to the FAA, “By identifying hot spots, it is easier for users of an airport to plan the safest possible path of movement in and around that airport. Planning is a crucial safety activity for airport users — both pilots and air traffic controllers alike. By making sure that aircraft surface movements are planned and properly coordinated with air traffic control, pilots add another layer of safety to their flight preparations. Proper planning helps avoid confusion by eliminating last-minute questions and building familiarity with known problem areas.”

Hard Lessons

Many rules we fly by resulted from lessons learned the hard way.

Among pilots, rules and regulations are often described as having been “written in blood.” The implication being that the regulation under discussion likely came about as a result of an accident or incident where, had the regulation existed at the time, the outcome may have been different. This is often accurate to varying degrees, and the notion can be a reminder to pilots that “[i]n this business we play for keeps,” as Ernest K. Gann wrote in his classic Fate is the Hunter.

The factors that have contributed to accidents and near-accidents help shape FAA guidance covering most aspects of our day-to-day flight operations. These changes can range from major updates to the FARs to seemingly minor details of procedure charting and radio phraseology. Considering that changes to FAA regulations and guidance often take place over the course of several years—or even decades—it can be difficult to tie a rule change back to a specific mishap, or group of mishaps.

However, sometimes a specific mishap leads directly to a change, or serves as a tipping point to effect change after similar mishaps have occurred. In these cases, we are given the opportunity to see the safety impact of the rule. A brief look at three such mishaps, each of which led directly to rules and procedures we’re all familiar with, should be instructive.

Cleared For The Approach

Instrument approach procedures leave little margin for error, so it’s essential that pilots and controllers have the same expectations about how they are to be flown. Thankfully, modern FAA guidance and procedures for pilots and controllers alike provides little room for misunderstanding. It took the fatal crash of a Trans World Airlines Boeing 727-231 operating as TWA Flight 514 to make these expectations as clear as they are today.

At around 1100 local time on December 1, 1974, TWA514 was beginning its approach into the Washington Dulles International Airport (KIAD) outside Washington, D.C. The three-holer was vectored onto the 300-degree radial of the Armel VOR/DME—which is sited at KIAD and serves as the final approach course for the airport’s VOR/DME Runway 12 approach procedure—and given a descent to 7000 feet. While the flight was 44 nm from the airport, ATC said, “TWA514, you’re cleared for a VOR/DME approach to Runway 12.”

The captain of TWA514, apparently under the mistaken assumption the lack of an altitude assignment permitted an unrestricted descent to the final approach fix crossing altitude, initiated a descent to 1800 feet msl upon receiving the flight’s approach clearance. This was despite the fact that the approach procedure depicted a minimum safe altitude of 3300 feet for the sector in which the 727 was flying, as well as multiple nearby feeder routes with minimum altitudes ranging from 3000 feet to 3700 feet. The aircraft crashed into the west side of Mount Weather, near Berryville, Va., 25 nm northwest of Dulles. There were no survivors.

Even though the arrival radial corresponded to the final approach course, because of the aircraft’s distance from the airport it was not considered to be on a segment of the approach by ATC and therefore was proceeding on its own navigation. According to ATC standards at the time, non-radar arrivals like TWA514 were not given an altitude assignment in approach clearances and were responsible for their own obstruction clearance. However, official guidance for pilots receiving such a clearance was vague, and had been a known concern within the FAA. In fact, TWA itself had expressed to the FAA concerns about the consequences of potential misinterpretation of these instructions four years before this accident.

Following the TWA514 accident, the FAA quickly revised pilot and controller guidance and implemented the radio phraseology we know today. In a similar situation today, an appropriate approach clearance might be something like, “Four miles from Lima. Turn right heading three-four-zero. Maintain two thousand until established on the localizer. Cleared I−L−S Runway Three-Six approach.”

Although ground proximity warning systems (GPWS) existed at the time of the accident, the majority of commercial aircraft were not equipped with it, according to the FAA. That changed quickly, too. Some additional changes resulting from the TWA514 accident are listed in the sidebar on the previous page. It’s now unmistakable that pilots are expected to adhere to their last assigned altitude until becoming established on a published portion of the instrument approach procedure.

Kilo Mike

Pilots flying today benefit from several years of emphasizing standardized radio phraseology and runway incursion awareness. For most pilots, it’s become second nature to read back ATC instructions entirely, particularly those involving taxi instructions and runway assignments. This wasn’t always the case. Not all that long ago, radio transmissions were less-standardized and readback procedures were more casual, making it easier for mistakes to go unchecked. A fatal runway incursion between a TWA MD-82 (TWA427) and a Cessna 441 Conquest (N441KM), changed all that.

At around 2140 local time on November 22, 1994, N441KM landed on Runway 30R at the Lambert-St Louis International Airport (KSTL) in St. Louis, Mo., and dropped off passengers at the FBO. Runway 30R is one of the primary runways at KSTL. At 2155, after the quick turn at the FBO, N441KM requested and was given its IFR clearance. At 2158 N441KM advised ground control it was ready to taxi. The ground controller responded, “One Kilo Mike, roger, back-taxi into position hold Runway Three-One, let me know this frequency when you’re ready for departure.” The 441’s pilot acknowledged the instructions, simply stating, “Kilo Mike.”

At the time, Runway 31—a shorter runway near the FBO—was used primarily for general aviation and commuter operations for departures. But instead of taxiing to Runway 31, N441KM proceeded to taxi into position and hold on Runway 30R at its intersection with Taxiway R.

Meanwhile, TWA427 was holding short of Runway 30R. The flight was given its takeoff clearance (the runway assignment of which also was not read back) and N441KM was told to continue holding “on Runway Three-One.” Again, N441KM responded only with “Kilo Mike.” The MD-82 began accelerating on Runway 30R, unknowingly bearing down on the Conquest holding at Taxiway R. Three seconds before impact, the cockpit jumpseater aboard TWA427 spotted the aircraft on the runway. The crew then aborted the takeoff and attempted to veer away from the aircraft, but the right wing of the MD-82 sliced through the fuselage of the Conquest, killing both aboard.

The diagrams above illustrate the basic differences between flying a non-precision approach with a so-called “dive-and-drive” procedure (top) and a constant-angle descent (CANPA). While the dive-and-drive might get you in when clouds are present at the bottom of the CANPA descent, flying a stabilized approach always is the smarter choice.

This accident directly resulted in several changes to ATC procedures and radio phraseology, as well as an increased emphasis on runway incursion awareness. The AIM and other guidance for pilots were updated to require pilot readbacks of ATC clearances containing runway assignments “as a means of mutual verification.” The FAA’s ATC handbook, Order 7110.65, was similarly updated to require controllers to obtain this readback. Indeed, the ATIS broadcasts airports at towered airports large and small often include a reminder to read back hold-short instructions.

As evidenced by the TWA427 accident, responding to an instruction with “roger,” “wilco” or a callsign, without reading back the instruction, does not confirm to ATC the message was correctly understood. Requiring readback of runway assignments seems like such a small detail but, had it been a requirement, this mishap likely would have been prevented. Unfortunately, more than 20 years later, it’s not uncommon to hear lazy pilots acknowledge an ATC clearance with their callsign only, and for lazy or busy controllers to not call them on it.

Dive and Drive

Instrument pilots have traditionally flown non-precision approaches, which by definition lack vertical guidance, using the “dive and drive” method. This technique has the aircraft quickly descending to the minimum descent altitude (MDA), and then flying level at the MDA until reaching the missed approach point (MAP). For years, these type of approaches have had a significantly higher accident rate than precision approaches and their stable descent along a glidepath. A non-fatal accident involving the controlled flight into terrain of an American Airlines MD-83 (AAL1572) resulted in changes to instrument procedures to improve the safety of non-precision approaches.

Shortly before 0100 local time, AAL1572 began the VOR Runway 15 approach to the Bradley International Airport (KBDL) in Windsor Locks, Conn. Flying through heavy rain and moderate turbulence, the crew weaved down the final approach course, trying to cope with a strong crosswind. After passing the final approach fix, the captain initiated a 1100-fpm descent and the first officer began to looking for the airport. With his attention devoted outside the cockpit, the first officer did not notice that the captain had descended below the MDA until the aircraft was already 309 feet too low.

Shortly thereafter, the aircraft struck trees on a ridgetop approximately 2.54 nm from Runway 15’s threshold. Immediately after impact, the captain initiated a go-around. With the left engine failed and the right engine only providing partial power, and with damage to the flaps and leading edges of both wings, the airplane limped toward the airport, crashed into an ILS antenna array just short of the Runway 15, and rolled onto the runway. Amazingly, only one passenger received minor injuries.

As a result of this accident, the vertical descent angle (VDA) for the final approach segment of non-precision approaches began to be included on published instrument approach procedures. This seemingly tiny change has facilitated constant angle of descent non-precision approaches, or CANPA (also known as continuous descent final approaches, or CDFA). Unfortunately, using the VDA is not mandatory and, as shown by the 2013 crash of UPS1354 in Birmingham, Ala., the dive-and-drive method is still in use.

With information on the published VDA, avionics manufacturers now can depict vertical path information on non-precision approaches, similar to depictions of precision approaches, allowing more-stabilized descents. While this is primarily found in larger aircraft, if you have ever flown a non-precision RNAV (GPS) approach to LNAV minimums with advisory vertical guidance (LNAV+V) in a light aircraft, you are relying on data generated from the vertical descent angle.

Are We Learning Yet?

Aviation accidents are nearly always complex events with multiple causal factors. The discussion of the accidents presented here is not intended to be a complete summary of all the relevant causes and findings. That’s what the NTSB, the investigative process and final reports are for. Instead, our focus is on how a single factor has impacted our modern aviation environment and to hopefully put a story behind the abstract notion of rules that are ‘written in blood.’

Lee Smith, ATP/CFII, is an aviation consultant and charter pilot living in Maryland.