N5155QCessna 172M · 1973

On August 29, 2011, about 1427 Pacific daylight time, a Cessna 172M, N5155Q, impacted a tree and the side of a private residence nearly 0.2 miles west of the departure end of runway 21 at the Santa Monica Municipal Airport (SMO), Santa Monica, California. The accident occurred during a Federal Aviation Administration (FAA) air traffic control tower controller issued go around maneuver that followed the pilot’s high and fast approach to the runway. During the impact sequence, the airplane was substantially damaged when the engine and instrument panel were displaced in upward and aft directions, thereby impinging upon the occupiable space in the cockpit. The pilot was seriously injured. The home was not occupied at the time of the collision. However, two of the three painters who were working outside the home sustained minor injuries. The student pilot had rented the airplane from the Santa Monica based flight school, Justice Aviation, for a planned solo instructional cross-country flight to Santa Barbara, California. The flight was performed under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The airplane departed SMO about 1423.

The student pilot reported to the National Transportation Safety Board investigator that he had been authorized by his Justice Aviation certified flight instructor (CFI) to perform the solo flight. After completion of an unsupervised preflight inspection of the airplane and finding it airworthy, he taxied for takeoff. Following completion of the customary pretakeoff checks, at 1422:39 a SMO FAA air traffic controller cleared the pilot for takeoff.

According to the student, the takeoff ground roll was accomplished without his awareness of a problem, and the airplane became airborne. Following customary procedures, a few seconds after liftoff the student looked at the airspeed indicator. He stated to the Safety Board investigator that almost immediately he observed that the airspeed indicator was malfunctioning. The indicator’s needle, which displays the airplane’s indicated airspeed, suddenly increased and then decreased until reaching zero miles per hour (mph). At the time, the student believed that the airplane was flying over 60 mph, and was in a climb attitude.

At 1423:38, the student pilot informed the SMO air traffic controller that he had experienced an airspeed indicator failure, and wanted to return for landing. About 1 minute later, the controller cleared the pilot to land on runway 21, from which he had just departed.

The student proceeded to climb the airplane into the traffic pattern. The student reported to the Safety Board investigator that he was nervous, and he did not fly normal base and final approach legs. Rather, he kept the airplane closer to the runway than customary. This action resulted in the airplane being higher than normal on short final approach. The student stated that, although he partially extended the wing flaps in accordance with his training, the airplane was higher than normal as it crossed over runway 21’s landing threshold. Because the runway is nearly 1 mile long, the student opined that he would be able to descend over the runway and successfully land.

As the airplane approached the last 1/4 of the runway it was, according to both the pilot and the SMO controller-in-charge, about one wing span above the runway’s surface. As the pilot was attempting to land on the remaining runway, at 1426:36 a SMO controller directed him to go around.

The student pilot further reported to the Safety Board investigator that he acknowledged the air traffic instruction, raised the wing flaps, and pushed the engine’s throttle full forward to obtain engine power. Thereafter, the student observed power lines in front of the airplane, and he maneuvered right and left to avoid them.

The student pilot held a first class medical and student pilot certificate that was issued on December 16, 2010. At the time of the accident, he held approximately 48 total flight hours, all accrued in the accident airplane make/model. About 13 hours were operating as pilot-in-command.

Interviews with the student pilot and his certified flight instructor (CFI) revealed that the CFI did not use a standard syllabus or training plan when he instructed students. Although the CFI taught the student pilot to check the pitot tube, he did not instruct him to check the small drain hole. Additionally, the CFI instructed his students to never use 40 degrees of flaps during landing unless it was absolutely necessary. The student pilot recalled practicing one type of stall with his CFI, which included the CFI adding engine power and pitching the nose upward. Neither the student pilot nor the CFI owned the pilot operating handbook for the airplane, and they used a standard checklist that was kept in the airplane.

According to the Cessna Aircraft Corporation, the accident airplane's wing span is 36 feet 1 inch. The Cessna “Owner’s Manual” for the model 172M indicates that when flying at the airplane's maximum certificated gross weight, under standard atmospheric conditions, with 40 degrees of wing flaps extended and no headwind, the airplane can be stopped in a ground roll distance of 520 feet. From 50 feet above the ground, the airplane can land and stop in a total distance of about 1,250 feet. The Owner’s Manual notes that these distances may be reduced 10 percent for each 5 knots of headwind. Given the reported 8-knot direct headwind at the time of the accident, the referenced distances are reduced by about 16 percent.

According to the air traffic controllers that viewed the accident airplane's flight path over the runway, the instruction to go around was issued to the pilot when he was flying about one wing span's height above runway 21 and was overflying the intersection of runway 21 at A2/B2. This location is about 1,150 feet from the end of the runway. The Safety Board investigator notes that about 75 additional feet of paved surface exist before the paved surface ends and the terrain slopes downward. The air traffic controllers reported that, at the time of the event, the wind was from 210 degrees at 8 knots.

An air traffic control specialist reviewed the air traffic control information related to the flight.

At 1421:27, the pilot contacted the SMO tower local controller (LC) position and requested a shoreline departure to SBA with Visual Flight Rules (VFR) flight following. At 1421:39, the tower controller informed the pilot “…I can give you a frequency airborne, or if you want a squawk off of the ground it’s gonna be a little delay, which would you prefer?” The pilot informed the tower he could wait until he was airborne. At 1422:09, the SMO tower controller approved a shoreline departure, and instructed N5155Q to “line up and wait, be ready to go Cessna 1 mile left base.” At 1422:38, the controller cleared the pilot for takeoff. The pilot acknowledged the clearance, and departed SMO airport.

At 1423:38, the pilot of N5155Q transmitted, “…my airspeed indicator doesn’t seem to be working here, uh, I need uh to go around and land please.” The LC instructed the pilot to make left traffic for runway 21. At 1423:54, the SMO tower controller transmitted “Cessna 55Q is, do you need further assistance, is everything OK?” The pilot of N5155Q responded “uh, just my airspeed indicator doesn’t seem to be uh working here.”

At 1424:34, the local controller transmitted, “Cessna 55Q wind two-three-zero at niner runway 21 cleared to land.” The pilot responded, “cleared to land uh runway 21 55Q.”

At 1426:12, N5155Q crossed the approach end of runway 21. The airplane remained airborne for approximately 3,800 feet down the runway to the A2/B2 intersection. When interviewed, the LC said that at the time he believed N5155Q was too high, and that there was not sufficient runway remaining from the A2/B2 intersection to the end of the runway for the airplane to safely land. At 1426:36, the local controller transmitted, “Cessna 55Q start a climb, go around.” The pilot responded, “going around 55Q.” At 1427:08, an unknown aircraft transmitted over the SMO frequency “(unintelligible) the Cessna just went off at the end.” The LC responded that he was contacting the fire department. Beginning at 1428:09, the LC made four unsuccessful attempts to contact N5155Q on the SMO tower frequency, with the final attempt occurring at 1430:18. During the attempted go-around, N5155Q impacted trees approximately 900 feet west of the departure end of runway 21, and subsequently collided with a house. The pilot was seriously injured, and 2 persons on the ground received minor injuries as a result of the accident.

The Safety Board investigator’s on scene examination of the accident site revealed that the airplane initially collided with a tree located about 900 feet west of the departure end of runway 21. The estimated elevation at the point of impact was 100 feet mean sea level (msl). The elevation at the departure end of the runway was 118 feet msl. The distance between the impacted tree top and the main wreckage, located partially on top of a block wall, was about 85 feet.

The airplane was recovered from the accident site, and an examination of its airframe structure and engine has been concluded. The pitot tube was found blocked by debris between the ram air inlet and the drain hole. No additional mechanical anomalies were identified.

Engine and Propeller Examination

The crankshaft was rotated through 360 degrees and thumb compression was observed in all cylinders, and no anomalies were noted as the accessory gear rotated. Several of the spark plug leads were observed crushed and torn, and no spark was noted when the magnetos gears were rotated. The top spark plugs were removed, and exhibited normal combustion signatures, according to the FAA airworthiness inspectors participating in the examination. The carburetor was found broken from its attachment in an impact-damaged area of the engine case. The carburetor, gascolator, and wing tank fuel screens were devoid of obstructing debris. The propeller was found attached to the engine. It exhibited forward and aft bending and chordwise scratches on its cambered surface.

Pitot Tube Examination

The pitot tube and internal debris was sent to the NTSB Materials Laboratory for further examination. A visual examination under magnification (using a 5x to 50x stereo zoom microscope) of the material removed from the pitot tube revealed light brown/tan granular particulates similar in morphology to sand or soil.

The material was examined by an entomologist to determine if any insect activity (nesting, etc.) had occurred in the pitot tube. The entomologist determined that a small amount of insect cuticle (the outer skeleton of arthorpods, including insects) was present in the sample, but was too damaged to be identified. Due to the small amount of insect cuticle present as well as the absence of other signs of nesting (eggs, larvae, etc.) in the provided material, it was not likely that insects had been nesting in the pitot tube.

A sample of the material was examined by scanning electron microscopy (SEM) and quantitative standardless energy dispersive x-ray spectroscopy (EDS) in accordance with ASTM E15082. The EDS analysis of representative particulates showed the presence of aluminum, silicon, oxygen, magnesium, and iron. These constituents are consistent with elements found in sand or soil.

The internal surfaces of the pitot tube were examined using a boroscope. No noticeable marks or debris were found on the internal surfaces of the tube. The nozzle of the pitot tube was sectioned along the longitudinal centerline to inspect the interior. A small space between the nozzle head and the threaded portion of the tube was found. A small amount of material was found adhered to the top of the threaded portion of the tube. The material on the top of the threads was similar in color and morphology to the submitted material. SEM/EDS analysis of representative particulates showed the presence of aluminum, silicon, oxygen, magnesium, and iron, which was the same as the submitted material.

According to the Cessna Pilot Safety and Warning Supplements, “If the pitot tube ram air inlet becomes blocked, the airspeed will drop to zero. If this blockage cannot be removed in flight, the pilot must rely on pitch attitude and power settings to maintain safe airspeed. A slightly higher than normal power setting should be used to maintain a reasonable margin of extra airspeed on final.” The Cessna pilot operating handbook (POH) for the airplane recommends extension of wing flaps to 40 degrees for short field landings.

The FAA Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25A), Chapter 7, states, in part, “The pitot system can become blocked completely or only partially if the pitot tube drain hole remains open. If the pitot tube becomes blocked and its associated drain hole remains clear, ram air no longer is able to enter the pitot system. Air already in the system vents through the drain hole, and the remaining pressure drops to ambient (outside) air pressure. Under these circumstances, the ASI (airspeed indicator) reading decreases to zero, because the ASI senses no difference between ram and static air pressure. The ASI no longer operates since dynamic pressure cannot enter the pitot tube opening. Static pressure is able to equalize on both sides since the pitot drain hole is still open. The apparent loss of airspeed is not usually instantaneous but happens very quickly."