History of Flight
On September 19, 2014, about 0847 central daylight time, an Embraer EMB-505 Phenom 300 airplane, N322QS, impacted a ditch after departing the end of the runway while landing at Lone Star Executive Airport (CXO), Conroe, Texas. Neither of the two airline transport-rated pilots was injured. The airplane was substantially damaged. The airplane was being operated by NetJets Aviation, Inc., as a 14 Code of Federal Regulations Part 91 positioning flight. Instrument meteorological conditions existed at the airport at the time of the accident, and an instrument flight rules flight plan had been filed. The flight originated from Nashville International Airport, Nashville, Tennessee, at 0706.
According to the dispatch flight release paperwork, the pilot-in-command (PIC) and second-in-command (SIC) planned to land on runway 14, which was assumed to be wet. Before the flight, notices to airmen (NOTAMs) had been issued, stating that the runway 14 threshold had been displaced 3,377 ft and that the instrument landing system (ILS) and RNAV instrument approaches were not available. Although the NOTAMs were included in the flight release paperwork, dispatch personnel overlooked them, resulting in flight planning numbers predicated on the full length of runway 14.
According to cockpit voice recorder (CVR) information, at 0827:04, the pilots received the automatic terminal information service (ATIS) information, which indicated that the runway 14 takeoff and landing distance was 4,111 ft and that the ILS for runway 14 was out of service. The pilots calculated the runway length required for a wet runway landing and then chose to land on runway 1, which was the longer runway. The PIC stated that, during the approach, the flight encountered light rain but that the rain was moving from the northwest to the southeast, away from the airport and that this alleviated any concern about standing water on the runway. He added that both he and the SIC had previously landed the EMB-505 in moderate-to-heavy rain with no decrease in braking ability.
The CVR recorded the pilots briefing the approach and missed approach procedures. Subsequently, the tower controller cleared the runway 1 RNAV approach, and the pilots then discussed alternate airports in the area. At 0841:30, the tower controller cleared the airplane to land and stated that moderate-to-heavy rain was at the airport. The pilots conducted the Before Landing checklist and continued the approach. While continuing the approach with the SIC flying the airplane, they saw the runway at 600 ft above ground level, and the copilot disengaged the autopilot at 400 ft. At 200 ft, the SIC reduced the power and adjusted the altitude and airspeed for a stabilized approach with a maximum airspeed during the approach of 130 knots.
In his postaccident written statement, the PIC stated that the landing appeared normal and "smooth." The SIC stated that he began braking with half pressure and continued to increase the brake pressure to maximum, which was the normal braking procedure. Sounds recorded on the CVR consistent with the airplane touching down were heard at 0837:13, followed by the pilots stating that the airplane was not slowing down. The SIC stated, "brakes. Emergency brakes," followed by "nothin' man" and "I got nothin'." The PIC stated "where's the brakes," followed by "where are they?" The PIC then said "go…don't go sideways, don't go sideways." The airplane exited the departure end of the runway and continued about 400 ft through soft/muddy terrain before coming to rest half-way down a ditch.
According to the air traffic controller who witnessed the accident, the pilots flew the RNAV runway 1 approach and broke out of the clouds at the minimums for the approach. The controller stated that the airplane touched down just past the 1,000-ft marker on the runway and did not appear to decelerate as it continued down the runway.
Personnel Information
PIC: The PIC held an airline transport pilot certificate with an airplane multiengine land rating and a commercial pilot certificate with airplane single-engine land and balloon ratings. He held type ratings in Cessna 500, 650, and 750; Embraer 505; and Hawker Siddeley HS-125 airplanes. A limitation on the EMB-505 type rating was the requirement of an SIC. His last flight check was in the EMB-505 on May 12, 2014. He was issued a first-class FAA medical certificate on April 3, 2014, which contained the limitations that it was not valid for any class after October 31, 2014, and that he must wear corrective lenses. He had 13,466 hours of flight time, of which 322 hours were in EMB-505 airplanes.
SIC: The SIC held an airline transport pilot certificate with an airplane multiengine land rating and a commercial pilot certificate with an airplane single-engine land rating. He held type ratings in ATR-42, ATR-72, Cessna 750, Bombardier CL-65, and Embraer 505 airplanes. Limitations on the CL-65 type rating were SIC privileges only and circling approaches in visual meteorological conditions. A limitation on the EMB-505 type rating was the requirement of an SIC. His last flight check was in the EMB-505 on May 12, 2014. He was issued a first-class FAA medical certificate on July 22, 2014, with no limitations. He had 9,861 hours of flight time, of which 361 hours were in EMB-505 airplanes.
Aircraft Information
The accident airplane was a twin-engine turbofan, low-wing airplane, serial number 50500165, manufactured in 2013. It was type certificated as a 14 CFR Part 23 commuter category airplane and configured for two flight crewmembers and seven passengers. The airplane was equipped with two Pratt & Whitney PW535E turbofan engines, each delivering 3,360 lbs of thrust. It was maintained in accordance with the manufacturer's inspection program; the last inspection was completed on July 2, 2014, at a total airframe time of 597.7 hours.
Brake System: The airplane's hydraulic brake system delivered hydraulic pressure via input from brake pedals. The SIC (right seat) brake pedals were mechanically linked to the PIC (left seat) brake pedals. Each PIC brake pedal was connected to a pedal position transducer (PPT) that produced electrical outputs to the brake control unit (BCU). The BCU controlled the main brake system, a brake-by-wire system with an antiskid function. The only pedal force feedback was from a force spring providing consistent resistance regardless of runway condition. Wheel speed information came from two axle-mounted speed transducers. The antiskid function controlled slip ratio and had locked-wheel protection. The airplane was equipped with an emergency parking brake (EPB) operated by a T-handle, mechanically linked via steel cable; antiskid was not available with EPB. An examination of the brake system and BCU data indicated that the brake system functioned as commanded during the landing.
Ground Spoiler Function: The airplane had a ground spoiler function that deployed spoilers on the ground during landing to decrease lift, increase drag, improve braking, and reduce stopping distance. The ground spoilers must be armed, the airplane on the ground, and thrust levers in idle for deployment. The function automatically armed when weight-on-wheels sensors indicated "in-air" for more than 10 seconds and airspeed greater than 60 knots.
Certification: 14 CFR Part 23 regulations require dry-runway landing distances to be published; certification does not require publication for wet or contaminated runways. The EMB-505 was first certificated by the Brazilian regulator, which does not require wet runway distances. However, for European certification, Embraer proposed unfactored wet-runway landing distances as 125% of unfactored dry distances; EASA accepted. Factored wet-runway distances in the AFM were 115% of factored dry distances, or 192% of unfactored dry distances. The AFM also provided tables for standing water, slush, or wet snow at depths of 0.125, 0.250, and 0.375 inches.
Meteorological Information
At 0841, the CXO automated surface observation system reported calm wind, visibility 2 miles in heavy rain and mist, few clouds at 500 ft agl, ceiling 8,000 ft agl broken, 10,000 ft agl overcast, temperature 23°C, dew point 22°C, altimeter 29.93 inHg. Remarks: hourly precipitation 0.21 inch, temperature 22.8°C, dew point 22.2°C. Rain began at 0444, varied moderate to heavy from 0725 until after the accident, ended at 1129. Total precipitation between 0444 and 0847 was 0.45 inch; between 0444 and 1129 was 0.50 inch.
Airport Information
CXO is located about 37 miles north of Houston, Texas. The airport has an air traffic control tower operational between 0700 and 2200. Elevation 245 ft, magnetic variation 5° east. Runway 1/19 is 5,000 ft long, 100 ft wide, concrete, good condition, threshold elevation 230 ft, 0.2% grade. It has medium-intensity approach lighting and nonprecision runway markings; a two-light precision approach path indicator was out of service. Runway 14/32 was under construction; a NOTAM had displaced the threshold 3,377 ft and made ILS and RNAV approaches unavailable.
The dispatch Flight Release for N322QS planned landing on runway 14 (assumed wet). NOTAMs were included but overlooked by dispatch. The pilots became aware during flight and opted for runway 1. ATIS ZULU reported runway 14 takeoff/landing distance 4,111 ft and ILS out of service.
Wreckage and Impact Information
According to the FAA inspector, light tire scuffmarks on runway 1 began 1,877 ft before the departure end. No visible rubber transfer. The airplane exited the runway and continued about 400 ft through soft/muddy terrain before coming to rest on down-sloping terrain. Distance between nose tire and right main landing gear track was 18 inches, indicating skidding after departing runway. Flat worn spots on both main tires; both showed evidence of reverted rubber hydroplaning. The airplane contacted a silt/erosion control fence; nose landing gear collapsed and separated just before rest. Substantial damage included forward bulkheads, composite ribs, forward fuselage frame, and center fuselage area. After the accident, ground hydraulic power was applied (2,850 psi); brakes and spoiler system tested normally; antiskid auto-startup test with no faults.
Tests and Research
BCU and Central Maintenance Computer (CMC): The BCU was removed and functionally tested at Meggitt in the UK, functioning normally. Embraer downloaded CMC messages on scene. Although four sequences of faults and messages were recorded, data and brake system examination indicated the brake system functioned as commanded during landing.
Flight Recorders: The airplane had an L-3/Fairchild FA2100-3083 combination cockpit voice and flight data recorder (CVDR), serial 000885510. CVR contained 2 hours 4 minutes 14 seconds of good quality audio; a transcript was prepared from 0824:47 to 0848:01. FDR contained 222 hours of data; the accident flight was the last flight, duration about 1 hour 37 minutes.
FDR Data: FDR data showed the airplane on approach above 150 knots. From 0844:18 to 0844:38, flap position increased through to flap 3, remaining for rest of approach. At 0844:43, brake pressure briefly spiked to about 3,000 psi then returned to 0; pilot brake pedal position near 0. Approach speed decreased to about 130 knots on short final. At 0847:09, brake pedal position parameters became active and increased just before touchdown. One second later, main wheel spin activated and increased. Two seconds later, speed brakes began extending, reaching maximum at 0847:14. About same time, all weight-on-wheels discretes became true. Between 0847:14 and 0847:24, brake pressure for both MLG remained below 1,000 psi; pedal positions increased to about 36 mm as airspeed, groundspeed, and wheel speed decreased. At 0847:24, EPB discrete became active; immediately brake pressure plateaued near 3,000 psi and wheel speed decreased to about 0 knots. Between 0847:27 and 0847:42, brake pressure remained about 3,000 psi; pedal positions steady about 35 mm as KIAS and groundspeed decreased. At 0847:24, a brake fail indicator activated as brake pressure dropped to 0 psi and pedal positions remained near maximum while airplane experienced tri-axis acceleration changes consistent with departing runway. KIAS and groundspeed dropped to about 0 knots; speed brake surface positions decreased to 0. Recording ended at 1347:59 with airplane at rest.
Airplane Performance Study: The NTSB conducted a study to determine airplane position, orientation, and responses. The approach complied with stabilized criteria; airplane crossed threshold at 121 knots (9 knots faster than Vref) and 45 ft above runway, touched down about 903 ft from threshold at 118 knots groundspeed. Headwind negligible. After touchdown, pedal deflections progressively increased to maximum braking in about 11 seconds; maximum deceleration -0.17 G at 0847:17 (about 7 seconds after touchdown). Between 0847:19 and 0847:22, deceleration increased briefly then decreased until about 0847:23.5 (13.5 seconds after touchdown), as wheel speeds decreased to 0, consistent with EPB application and locked-wheel skid. Wheels remained locked until stop. Deceleration increased steadily then decreased as airplane passed end of runway at 0847:37.4. The airplane exited the runway about 27 seconds after touchdown at about 61 knots groundspeed.
The computed braking friction coefficient peaked at about 0.16 then decreased to about 0.06 after EPB application and locked-wheel skid. Even before EPB, the coefficient was lower than predicted by Part 25 wet runway models and lower than implied by EMB-505 POH wet runway distances. However, it was consistent with a NASA model based on CFME runway friction measurements. Tests on runway 1 at CXO measured macrotexture depth and cross slope; considering rainfall rate of 0.3 inch/hour, maximum water depth was about 0.006 inch, far below 3 mm for a "flooded" runway per EASA AMC 25.1591. Therefore dynamic hydroplaning was unlikely; low braking friction likely resulted from viscous hydroplaning.
The Phenom 300 QRH showed unfactored landing distances for weight 15,483 lbs and flaps 3: dry 2,541 ft, wet 2,922 ft, contaminated (1/8 in water) 4,885 ft. The performance study determined that if EPB had not been set and braking friction continued at early levels, the airplane would have stopped about 4,669 ft from threshold with 331 ft remaining. This stopping distance is close to the AFM contaminated distance of 4,885 ft, but runway characteristics and rainfall precluded that condition. The study concluded that the braking friction deficit showed stopping performance more consistent with AFM landing distances for runways contaminated with standing water than for simply "wet" runways.