# Gulfstream Aerospace Flight 153

Gulfstream Aerospace Flight 153 was a test flight with a Gulfstream G650 on the April 2, 2011. On that day, the aircraft encountered a flow disruption during takeoff leading to its crash, killing all four occupants.

## Background

For the certification of the Gulfstream G650, Gulfstream Aerospace maintained an ambitious flight test program. The manufacturer expected a certification of the aircraft type in the 3rd year. Quarter 2011.

### Aircraft

The aircraft involved, which took it’s first flight on February 25, 2010, was the second prototype of the newly developed Gulfstream G650 business aircraft with movement number 6002 (registered N652GD), owned by it’s manufacturer Gulfstream Aerospace. The aircraft was equipped with two Rolls-Royce BR700-725A1-12 engines. The aircraft had completed a total operating capacity of 434 operating hours up to the accident.

### Occupants

There was a crew of four on board the aircraft, consisting of two flight crew in the roles of Captain and First Officer, as well as two flight test engineers:
* The 64-year-old Captain had acquired a commercial pilot license after a career as a military pilot in April 1981 and was initially responsible for the Boeing 707 licensed. In January 1991 he was approved for Learjet. Between October 1997 and October 1998, he expanded his portfolio to training around the aircraft types Gulfstream V, Boeing 707 and 720, Grumman Gulfstream II, and he had been working as a test pilot for Gulfstream Aerospace since August 1997. He had 11,237 hours of flight experience, of which he had completed 237 hours in the cockpit of the Gulfstream G650. In the role of pilot in Command, he had completed 160 flight hours with aircraft of this type.
* The 51-year-old First Officer had received a commercial pilot license in July 1990 based on his flight experience as a military pilot. In November 2006, he received a model authorization for the Boeing 737. Between August 2007 and December 2009, he acquired further model authorizations for the aircraft typesIAI 1125 and Gulfstream V. He had 3,940 hours of flight experience, of which 140 hours were on the Gulfstream G650.

## Accident

On the day of the accident, a test was planned involving a single-engine start to simulate an engine failure. The objective of this maneuver was to assess the takeoff distance at minimal flap position during an engine failure scenario. The takeoff occurred at 9:34 a.m. Shortly after takeoff, the aircraft began to roll uncontrollably to the right. The Gulfstream made contact with the ground on its right wingtip and subsequently veered off the runway. The landing gear was sheared off, and the aircraft collided with a concrete structure and a weather station. It continued to slide along the ground and caught fire. Tragically, all four occupants lost their lives, and the aircraft was nearly completely consumed by the fire.

## Investigation

The National Transportation Safety Board took over the investigation into the cause of the accident. Three main causes were identified during the investigation:
* Gulfstream's failure to properly calculate and validate the take-off speeds for the flight tests and to detect and correct the V2 error during previous G650 flight tests.
* Increasingly aggressive attempts by the flight test team to reach V2 speeds that were set too low.
* Gulfstream's insufficient investigation of previous incidents during the test campaign (Flight 88 on 16. November 2010 and flight 132 on 14. March 2011), which indicated that the maximum angle of attack of the aircraft estimated by the company was too high in the ground effect.
Due to the exceeding of the incorrectly calculated critical angle of attatment, the right wing had a flow break. The two previous incidents had not been sufficiently investigated by Gulfstream, so that the final cause could only be determined after the crash. The tight test program specified by the company had also contributed to the accident on two of the three points: The test pilots tried to achieve the lowest possible V2 in order to achieve the take-off and landing distances already promised in advance and there was no time to get to the bottom of major errors.