High-Speed RTO`s - More than a handfull - BCA Digest

The Go/No-Go Decision: High-Speed RTOs Are Fraught With Risk

Jul 21, 2017Fred George | Business & Commercial Aviation

​Dann Runik still gets chills when he remembers the rainy morning of March 1, 1978. He was in the cockpit of a DC-8 at Los Angeles International Airport as he watched Continental Flight 603, a heavily laden DC-10, lumber down Runway 6R on its takeoff roll. The heavy trijet was bound for Honolulu with 198 passengers and crew aboard.

Everything appeared normal to the DC-10’s flight crew as the aircraft accelerated toward its 156 KIAS V1 go/no-go decision speed. But when passing through 152 KIAS, the crew heard a loud “metallic bang” and the jetliner started to “quiver.” The captain felt it was unsafe to continue the takeoff, so 4 kt. below V1 he initiated a rejected takeoff (RTO).

Unknown to the crew, a recapped tire on the left main mount had thrown a tread and had blown out. This caused an adjacent tire to become overloaded, causing it to blow as well. Shrapnel from either or both of the two ruptured tires pierced a third tire on the left main mount and it, too, failed. The aircraft both yawed and sagged to the left as a result. The crew felt as though they were losing control of the airplane.

Continental Flight 603 at Los Angeles International Airport, 1978 Credit: NTSB

The captain stood on the brake pedals, pulled the throttles to idle and yanked up on the thrust reverser levers. At 159 KIAS — 3 kt. above V1, the 429,000-lb. jumbo began to decelerate but at a considerably slower rate than the crew had experienced during high-speed RTO simulator training. The device had not been programmed to simulate braking performance compromised by blown tires.

On that day, though, the wet runway surface combined with the failed tires to severely reduce stopping performance, particularly due to the upwind end of the runway being heavily coated with rubber skid marks from aircraft landing to the west and the lack of pavement grooving. In fact, the conditions at the end of the runway impeded braking action by as much as one-third, a condition the crew likened to sliding on ice.

With 2,000 ft. to go on the 10,885-ft. runway, the captain realized he couldn’t stop by the end of the runway. So, he steered the aircraft right of centerline in an effort to avoid hitting the approach light stanchions. As the aircraft rolled off the pavement at nearly 70 kt., the left main mount broke through the tarmac of the overrun and partially sheared off its mount, trailing behind the wing. The left fuel tank ruptured and nearly 6,000 gal. of jet fuel burst into fire, engulfing the left side of the aircraft. The left wing dug into the ground, the aircraft spun almost 90 deg., and it came to a stop some 664 ft. off the runway, or nearly 1 mi. from the point at which the captain initiated the RTO.

The cabin crew immediately began evacuating the aircraft. But the intense heat from the fire on the left side soon made most of the slides on the right side fail. And one of the right over-wing exit slides failed to deploy at all. Less than two-thirds of the aircraft occupants were able to use the escape slides before all of them failed. The rest had to jump off the aircraft.

Three crewmembers and 11 passengers suffered serious injuries during the egress. Local firefighters also were injured in the inferno. Two passengers later died of their burns and smoke inhalation.

Similarly, on Sept. 19, 2008, a Learjet 60’s RTO in Columbia, South Carolina, resulted in the deaths of both pilots and two passengers, and caused severe burns to the two surviving passengers. This accident also involved the captain attempting a high-speed abort after the aircraft suffered tire failure. Contributing to the accident were malfunctioning thrust reversers that allowed the aircraft to accelerate well above the V1 decision speed as the captain attempted to stop the aircraft.

A close review of the facts suggests an RTO was the wrong decision in both accidents.

High-Speed Abort Risks

The relative rarity of RTOs is one reason that most pilots are unprepared to make the most informed go/no-go decisions when trouble suddenly imperils an aircraft during takeoff. Runik, now FlightSafety International’s executive director, advanced training programs, notes that for every 3,000 commercial jet departures, only one results in an RTO. But a Boeing study notes that many RTOs go unreported, so the actual number may be closer to one in 2,000 takeoffs, or greater.

Unreported events may include slow-speed aborts early in the takeoff roll, occasioned by warning lights, out of trim conditions or the aircraft not having the appropriate high lift configuration. Considering the relative infrequency of RTOs, business aircraft pilots might only experience such an event once every 10 to 20 years. With such low probability, there’s a high risk of startle factor should such an event occur. There is ample reason to be prepared for such events, however, considering the potential risks associated with RTOs.

Of the reported RTOs, fewer than one in 1,000 resulted in an overrun accident or incident in large part because the decision to stop the aircraft was made well below the V1 decision speed. Notably, more than three-quarters of all RTOs are initiated at 80 KIAS or less. Such relatively slow-speed RTOs seldom cause problems. RTO accidents and incidents mainly come from the 2% of RTOs initiated above 120 KIAS. Notably, 55% of high-speed aborts were initiated above V1. Of those, 79% resulted in fatalities or incidents.

You’re only likely to suffer an accident or incident from an RTO about once in every 4.5 million departures, according to FAA statistics. But the risks associated with high-speed RTOs were plenty sufficient to cause Runik and FlightSafety to team with Randy Gaston, Gulfstream Aerospace’s recently retired vice president, flight operations, to attack the problem.

Learjet 60’s RTO in Columbia, South Carolina, September 2008 Credit: NTSB

Historically, pilots have rejected takeoffs less than 18% of the time due to engine failure, according to the Netherlands Aerospace Center’s (NLR) Air Transport Safety Institute. The other four-fifths were due to blown tires, warning lights or other indications. However, less than half of those RTOs were warranted. And when pilots made the decision to continue the takeoff despite such abnormal indications, none of those “go” decisions resulted in accidents or incidents, according to FlightSafety’s research.

“There’s an overall lack in evidence-based training based on examining FOQA [flight operational quality assurance] data, NTSB accident reports and ASRS [NASA’s Aviation Safety Reporting System] incidents. It was Randy’s idea of teaching pilots how to make go/no-go decisions,” says Runik.

At first Runik balked. Gaston responds, “Oh sure. It’s too difficult. It’s too political. But since you’re carping about it, you’re the one to do it.

Runik says that most pilots are accustomed to making simple balanced field length go/no-go decisions, where the accelerate-go and accelerate-stop distances are equal at the V1 speed. That may suffice for most simulator training scenarios, but conditions are far more complex in real life. It would be valuable to look separately at accelerate-go and accelerate-stop distances, if the aircraft manufacturer were to provide the data. Instead of using a single V1 decision speed, it’s preferable to look at V1min, which is the slowest speed at which a one-engine-inoperative (OEI) takeoff may be continued and which will enable the aircraft to reach the V2 OEI takeoff safety speed and a 35-ft. screen height above a limited length runway. And then look at V1max, the highest speed at which the takeoff may be rejected that allows the aircraft to be stopped on the runway remaining. V1min is the go/no-go speed when runway length is critical. V1max is the go/no-go speed when runway length is not a
factor.

However, very few general aviation aircraft manufacturers provide separate accelerate-go and accelerate-stop performance data, let alone the computational tools to enable pilots to use the data effectively to boost takeoff safety margins.

Traditional simulator training also doesn’t factor in runway slope, non-uniform traction conditions along the runways, obstacle and terrain hazards in the overrun areas, and rubber deposits near touchdown zones that, when wet, can be nearly as slippery as black ice, according to Runik. Traditional simulator training also doesn’t include sudden runway incursions by other aircraft, vehicles or animals.

A plethora of such factors made it difficult for Runik and Gaston to come up with hard and fast rules that covered all decisions that might be covered by the proposed FlightSafety go/no-go decision takeoff safety training program. Yet, they determined that pilots had been aborting takeoffs for several reasons that weren’t critical, decisions that potentially put the aircraft and all aboard at risk.

For example, some Gulfstreams have as many as 42 red warning messages that could pop up on the crew alerting system screen. Few of the alerts require rejecting the takeoff. Most of those abnormalities could be handled in the air just as safely as when on the ground. A takeoff trim configuration warning might pop up at high speed during the takeoff roll as air loads increase on control surfaces. And it’s highly unlikely that a pitch trim runaway will occur unless it’s triggered by a pilot pitch-trim switch input. Such spurious warnings can cause pilots to abort takeoffs for non-safety-of-flight alerts.

In fact, a Boeing study determined that in 55% of all RTOs in jetliners, the result might have been an uneventful landing had the takeoff been continued.

After Runik and Gaston had discussed several scenarios, though, they came up with three valid reasons to reject takeoff: (1) loss of directional control, (2) engine failure and (3) safety of flight.

Loss of directional control leads the list because it can be a clear-cut reason to keep the aircraft on the ground. Runik cautions, though, that a sudden yaw at high speed may be due to a tire failure, an animal strike or degraded nosewheel steering that may be countered by prompt and assertive control inputs. However, depending upon aircraft speed, stopping distance available, runway condition and slope, and other factors, the go/no-go decision may not be clear-cut.

The decision to reject a takeoff due to engine failure also isn’t necessarily as clear as it might seem. A typical civil jetliner accelerates at 3 to 6 kt. per second. And most business jets, having stronger thrust-to-weight ratios, accelerate considerably faster. It can take 2 to 4 sec. to recognize, call out and initiate the RTO, thus the aircraft may accelerate as much as 10 to 20 kt., or more, before the RTO is initiated. This can result in an abort above V1.

The Flight Safety Foundation’s Mark Lacagnina says that V1 should be reworded “takeoff action speed” rather than “takeoff decision speed.” The decision to reject the takeoff should be made long before reaching the V1 takeoff action speed, the point at which deceleration for the abort is begun. Lacagnina, however, isn’t getting much traction in the aviation industry or airworthiness authorities for that alteration.

Rejecting takeoff because of safety of flight is perhaps the fuzziest of decisions because it encompasses so many rare, but potentially fatal, risks. Among them are high-speed aborts that may be required due to sudden runway incursions by other aircraft, large animals or vehicles.

Advanced RTO Go/No-Go Course

FlightSafety International and Gulfstream have introduced a new RTO training course for large-cabin Gulfstream aircraft. In parallel, Gulfstream has modified its recommended SOPs for flight crew briefings and making more informed go/no-go decisions. The training organization is embracing this philosophy and incorporating it into the Pilot Training Handbooks for all Gulfstream models.

The 4-hr. RTO course exposes each crewmember to 18 different V1 go/no-go decision scenarios, requiring the flight crew to either continue or reject the takeoff. Go decisions provide additional training for pilots to fly their aircraft in high-stress, emergency situations when they must guide the aircraft to a successful emergency landing. Previous simulator training hasn’t exposed pilots to such urgent emergency scenarios in which pilots have to fly their aircraft back to the departure or divert airports with a high level of aggressiveness to achieve a successful outcome. The training course provides each pilot with the opportunity to practice multiple emergency return scenarios to proficiency.

The joint venture with Gulfstream proved so successful that FlightSafety has entered into a similar arrangement with Dassault Falcon Jet to offer an RTO training course for Falcon 900EX and 2000EX/LX/LXS EASy aircraft. Offered at its Dallas and Paris Le Bourget centers, the program expands upon the pre-takeoff safety briefings set forth in Dassault’s Crew Operational Documentation for Dassault Easy Vol. 2 (CODDE 2) publication. Similar to the Gulfstream course, the Falcon program enables pilots to expand their knowledge and enhance skills to boost safety margins during this critical phase of flight.

The training outfit next will offer the program for the Embraer Lineage 1000, then the Legacy 450 and 500. Similar programs for Textron’s King Air 200, 250 and 350 turboprops are under consideration.

Regardless of aircraft type, the same factors go into go/no-go decision making, assuming the aircraft has certified OEI takeoff performance capabilities.

“Pilots need to plan ahead, consider what actually can trigger a red warning light,” says Gaston. “A minor integrated avionics malfunction, for instance, might trigger multiple spurious red CAS messages. And trim systems don’t just run away on their own. So, think about what you really would abort for.”

Consider the actual conditions at the departure airport. Imagine, for instance, you’re departing 7,838-ft. MSL Aspen’s Runway 33, an 8,000-ft. strip with a 2% downslope. Assume it’s dusted with fresh snow. Off the departure end, the terrain quickly plunges down to the bed of the Roaring Fork River. Running off the end of the runway after an RTO is fraught with risk. Gaston notes that the accelerate-stop distances published in most business jet flight manuals don’t include deceleration provided by thrust reversers. So, don’t count on help from the TRs during a high-speed RTO.

FlightSafety International is one of the first general-aviation training firms to offer such training. The instruction involves the type of high-level decision-making knowledge, preparation and planning that can save lives when making go/no-go decisions.