Honeywell Aerospace

When you look at a Boeing 737 at the gate that is waiting for its passengers without ground power, hot air shimmers behind the tail tip. A small gas turbine is running there, supplying the aircraft with electricity and compressed air – and with high probability it comes from Honeywell Aerospace. The supplier from Phoenix builds no aircraft of its own but is inside a large part of the fleets you see: in the tail of the 737 and A320, in the cockpits of Gulfstream and Citation, in the engine nacelles of Challenger, Learjet and Falcon. If you want to sort your sightings not only by type but also by technology, you can’t get around Honeywell.

One name, many ancestors

Honeywell Aerospace is the result of a long chain of acquisitions and mergers. The name comes from a maker of heating controls in Minneapolis, while the aviation technology came mainly from other companies. The oldest and most important root is Garrett: in 1936, Cliff Garrett founded a small supplier business in Los Angeles, from which the Garrett Corporation and its AiResearch division emerged. Garrett specialized in cabin pressure, climate control and small gas turbines – exactly the fields that still shape the core business today.

After the founder’s death in 1963, Garrett went to the Signal Companies. In 1985 Signal merged with the Allied Corporation, which three years earlier had taken over the traditional manufacturer Bendix. That created Allied-Signal with a large aviation division. In parallel, the old Honeywell Inc. bought Sperry Aerospace in 1986 – the company whose name is closely linked with gyroscopic instruments and early autopilots. In 1994 AlliedSignal added the turbine division of Lycoming.

In 1999, AlliedSignal finally took over Honeywell. Because the Honeywell name was better known, the combined group then operated as Honeywell International. A good quarter century later came the split: on June 29, 2026, aerospace was spun off as an independent company and listed on the Nasdaq. Since then there has been Honeywell Aerospace with the ticker HONA and, alongside it, the automation group Honeywell Technologies.

The APU: Honeywell in the tail of almost every jet

The auxiliary power unit is the Honeywell product that spotters meet most often without consciously noticing it. In most airliners it sits at the very back in the tail cone and is at its core a small gas turbine. On the ground it supplies electricity for onboard systems and compressed air for air conditioning and engine start. In flight it serves as a backup if a generator fails. When it runs and when the aircraft would rather hang on ground power is explained in the article APU, ground power and PCA.

According to Honeywell, the company has built more than 95,000 auxiliary power units to date, of which more than 36,000 are in service. The most important families for scheduled aviation:

In the Boeing 737 NG the 131-9 is standard, and the 737 MAX uses it too. That means: every 737 of Ryanair or Southwest Airlines that you see at the gate carries a piece of Honeywell in its tail. In the A320 family, airlines have a choice between Honeywell and a competing product; according to widely cited figures, the decision went to the 131-9 for about 60 percent of the aircraft. On the Airbus A350 the HGT1700 is on board.

One of the best-known APU stories takes place in New York. When both engines failed after a bird strike on US Airways Flight 1549 in January 2009, the crew started the A320’s 131-9. It supplied the onboard systems with power during the glide down to the ditching in the Hudson River – an example of how the inconspicuous turbine in the tail is more than a comfort feature for time on the ground.

TFE731: the business jet engine born from an APU

The probably best-known Honeywell engine has a special origin. Garrett developed the TFE731 in the early 1970s from the core of one of its own auxiliary power units. At the front sits a fan driven through a gearbox – an early geared turbofan concept, long before the principle became big in commercial aviation. The goals were low fuel consumption and little noise, both crucial for business aircraft that often depart from airports close to cities.

In 1972 the first production TFE731-2 came off the line, and from 1973 it flew in the Learjet 35/36 and in the Dassault Falcon 10. Numerous variants followed with about 3,500 to 4,750 pounds of thrust, or roughly 15.6 to 21 kilonewtons. More than 11,000 were built, and together they have accumulated more than 100 million flight hours. The TFE731 is in, among others:

• the Dassault Falcon 50 and the Falcon 900, each with three engines at the rear
• the Hawker 800 and its derivatives
• the Citation models III, VI and VII from Cessna
• several Learjet generations
• jet trainers such as the Spanish CASA C-101

For spotters, the TFE731 is above all a topic for classics. Many of these jets have been in service for decades and show up regularly at airports with a lot of private aviation. You will recognize the gritty sound of a Learjet 35 on takeoff right away after a few encounters.

HTF7000: the powerplant of the super-midsize class

The modern successor in the business jet world is the HTF7000. Under the project name AS907 it first ran in 1999, and in 2004 it got its present name. The fan measures about 87 centimeters, and the thrust is between about 29 and 34 kilonewtons depending on the variant (roughly 6,500 to 7,600 pounds). The engine has established itself above all in the so-called super-midsize class – jets that can manage transcontinental routes in the US or flights across Europe without a stopover.

The nice thing about it: on all these types there is no engine alternative. If you have identified a Challenger 350, a Challenger 3500, a Gulfstream G280, a Praetor 500, a Praetor 600 or a Citation Longitude, you automatically know that two Honeywell engines hang at the rear. Accordingly, you run into the Challenger 350 often at business aviation airports, and you also find this segment in the fleets of big fractional providers such as NetJets and Flexjet.

How to tell the various business jet families apart by fuselage, windows and tail is shown in the article Telling Gulfstream, Global, Falcon, Citation and Challenger apart.

Turboprops, regional jets and helicopters

Below the jet world, the TPE331 is Honeywell’s big name. Garrett first ran the turboprop in 1960, and it went into series production from 1963. With more than 13,500 units built and an output of roughly 430 to 1,230 kilowatts, it covers a wide range. Typical is the single-shaft design, which produces a very characteristic, high-pitched whine on start-up and on the ground – many spotters recognize a TPE331 with their eyes closed.

Among the best-known types with the TPE331 are the Dornier 228, the BAe Jetstream 31/32, the Fairchild Swearingen Metro, the CASA C-212 Aviocar, the Mitsubishi MU-2 and the Turbo Commander. The MQ-9 Reaper drone also flies with a version of this powerplant.

A special case are the four-engine regional jets from British Aerospace. The BAe 146 flew with the ALF502, its further development the Avro RJ with the LF507. Both engines originally come from Lycoming and came to AlliedSignal in 1994 with the purchase of the turbine division. Honeywell continues to support them today – an important point for the ever rarer RJ operators.

From the same Lycoming line comes the T55, which has powered the tandem-rotor helicopter CH-47 Chinook in various versions since the early 1960s. More than 6,000 were built. In addition there are smaller turboshaft engines such as the HTS900 and LTS101 for light helicopters, as well as the AGT1500, which does not fly but powers the US M1 Abrams battle tank.

Avionics: Honeywell in the cockpit

The second major area lies behind the instrument panel. Since taking over Sperry, Honeywell has been one of the major avionics manufacturers. The best-known product family is called Primus. The Primus Epic glass cockpit is the basis of the PlaneView cockpit of large Gulfstream jets and was used in the Citation Sovereign, among others; the older Primus 1000 is in the Citation XLS, for example. For the Gulfstream G500 and G600, Gulfstream developed the Symmetry Flight Deck with sidesticks and touchscreens together with Honeywell.

In the avionics market, Honeywell competes mainly with Collins Aerospace, with Garmin on smaller aircraft, and with Thales in Europe. The result is that one and the same type can have very different cockpits depending on the year of manufacture. Bombardier, for example, later replaced the older Honeywell equipment on its large Global jets with a system based on Collins technology. You see none of this from outside – at most when looking through the windshield on the apron. What is allowed and what is not when photographing in the cockpit is covered in the article Photos in the cockpit.

Safety systems that save lives

Some of the most important Honeywell products you never see, yet you benefit from them on every flight. The ground proximity warning goes back to the engineer Don Bateman, whose team developed it further over decades. The older version reacted only to height above ground and sink rate. The enhanced variant EGPWS, which came to market in the mid-1990s, additionally compares the aircraft’s position with a worldwide terrain database and therefore also warns when a mountain lies ahead of the aircraft.

The effect was enormous. Accidents in which an intact aircraft is flown into the ground used to be among the most common types of fatal accidents. After the introduction of the warning systems, they dropped sharply on large airliners. In the US, the aviation authority FAA has required such terrain warning systems since 2002 for newly built turbine aircraft with six or more passenger seats.

Add to that the IntuVue weather radar, which detects thunderstorms at long range, systems that warn of incorrect runway use, inertial navigation and flight data recorders – the “black boxes” that are analyzed after incidents. How the transponder works as the second building block of collision avoidance is explained in the article Transponder Mode A, C and S.

Where you meet Honeywell while spotting

You meet the APU wherever 737s, A320s and A350s stand at the gate – so at practically every commercial airport. More exciting for Honeywell fans, though, are airports with a lot of business travel. At Geneva Airport the business aviation apron is large, and from the observation deck you see Challengers, Falcons and Citations in high density. Paris Le Bourget Airport is Paris’s most important business aviation airport, Nice Airport fills with private jets in summer, and London Luton Airport also has a large share of business flights. You will find practical tips in the article Spotting business jets.

At trade shows and airshows, Honeywell is almost always present as a supplier, even if the aircraft bear the names of other manufacturers. The articles on the Paris Air Show at Le Bourget and the Farnborough International Airshow give an overview of the big events. At military displays, with a bit of luck you hear a Chinook with its T55 turbines or a trainer such as the Leonardo M-346 or the Aero L-159, both of which fly with the Honeywell F124 engine.

If you want to see the history live: the Pima Air & Space Museum in Tucson is in the same US state as Honeywell’s headquarters and shows many aircraft with Garrett and Lycoming powerplants. You will find a spot guide for the museum grounds under Pima Air & Space Museum in Tucson.

Honeywell compared with the big engine makers

On large airliners, GE Aerospace, Rolls-Royce, Pratt & Whitney and – through the CFM joint venture – Safran share the market for the main engines. Honeywell plays no role there. Its strength lies one class below: in business jets, turboprops, helicopters and trainers. With APUs the picture is reversed. Here Honeywell is one of the two big suppliers, and the most important competitor is the APU division of Pratt & Whitney.

That gives you a practical rule of thumb for your sightings: on airliners you find Honeywell mainly in the tail and the cockpit, on business jets and turboprops often under the engine cowling as well. How to tell the various engine designs apart in general is explained in the article How to recognize engines. And if you want to capture the sounds of a TFE731, TPE331 or a running APU, the article Recording engine sound helps.

Conclusion

Honeywell Aerospace is a manufacturer you rarely see directly and yet photograph constantly. The 131-9 in the tail of every 737 NG and many A320s, the HGT1700 in the A350, glass cockpits in Gulfstream and Cessna jets, and warning systems that have prevented accidents over millions of flight hours – all of it comes from Phoenix. The company becomes visible mainly on business jets and turboprops, where the TFE731, HTF7000 and TPE331 have shaped the picture for decades.

With the spin-off in June 2026, the name now stands for aerospace alone. For you as a spotter, nothing changes: if you know which types fly only with Honeywell engines, you identify many business jets faster – and for the rest, a cleanly noted registration helps, as always.